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Full text of "The nomenclature of petrology, with references to selected literature"

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IWIVER6II, or ' 






Harper's Library of Living Thought. 



"Red Book" No. 256. 



Ready in the early Autumn. 






D.SC. (LOND.), A.R.C.S., D.I.C., F.G.S., F.R.G.S. 

Demonstrator of Geology and Petrology in the Imperial College of Science and 

Technology, London 
Technical Geologist to the British Fire Prevention Committee 











A, French Petrographic Terms - - 243 

B. German Petrographic Terms 

(compiled by Miss J.-H. ROBERTSON) 247 

C. Greek Words and Prefixes - 257 

D. Latin Words and Prefixes - 263 

E. Classification Tables - - - 265 





SOME years ago I began the compilation of a card- 
catalogue of petrographic and associated terms, for 
the use of students in the Geological Department of 
the Imperial College of Science and Technology. 
Each card gave a brief description of the meaning 
(or meanings) of the term to which it was devoted, 
together with references to those papers on the sub- 
ject which were available in the departmental 
library of the College, a library which, thanks to 
the collections made by the late Professor J. W. 
Judd and others, is unusually rich in author's 
separates. As the catalogue grew, its general use- 
fulness became apparent; and a series of sugges- 
tions that it should be developed and published led 
me finally to the conclusion that such a course 
would not be unjustified. 

There are many geological glossaries in which 
petrological terms find a place, but they are for the 
most part old, and to-day they are but little used, or 


even 'known. 1 Several petrological books contain 
glossaries; notably Sir Jethro Teall's great work, 
British Petrography (1888), and J. R. Kemp's 
Handbook of Rocks. The latest edition of Kemp's 
book was published in 1918, and contains a wealth 
of information, particularly in relation to the older 
terms and the newer American terms. The only 
independent publication of the kind, however, 
appears to be the Lexique Petrographique of 
-Lcewinson-Lessing (Paris, 1901). This invalu- 
able work is now nearly twenty years old, and so 
luxuriant has been the growth of nomenclature dur- 
ing the last two decades, that the Lexique no longer 
serves as an adequate guide through the somewhat 
tangled forest of names. 

The complexity of petrological nomenclature at 
the present day is demonstrated by the following 
list, in which examples are given to illustrate the 
varying characters and principles on which names 
have been based from time to time. 

Classical : basalt, basanite, obsidian, porphyry, syenite. 
Popular : chert, cokeite, forellenstein, gabbro, gneiss, 

granite, greisen, halleflinta, loess, marl, minette. 
Structure: augen-gneiss, banket, cipolino, dermolith, folia- 

1 Among those examined for the purpose of this book are the 

following : 
G. Roberts : An Etymological and Explanatory Dictionary 

of the Terms and Language of Geology, 1839. 
D. Page : Handbook of Geological Terms, 1859 & 1865. 
W. Humble : Dictionary of Geology and Mineralogy, 3rd 

Ed., 1860. 

G. H. Kinahan : A Handy Book of Rock Names, 1873. 
B. von Cotta (Trans, by P. H. Lawrence) : Rocks Classified 

and Described, 1878. 
T. H. Oldham : Geological Glossary, 1879. 


tion, knotenschiefer, lithophysae, oolite, perlite, pudding- 
stone, rhyolite, schist, variolite. 
Texture : anamesite, aphanite, granulite, hornstone, lithoi- 

dite, pegmatite, rhomb-porphyry. 
Roughness : grit, trachyte. 
Colour : eclogite, graywacke, greenstone, leucocratic, leuco- 

phyre, melanocratic, melaphyre, muscovadite, troctolite. 
Lustre : euphotide, lamprophyre, pitchstone. 
Fusibility : eurite, pyromeride, tachylyte. 
Organic characters: coral-sand, crinoidal limestone, diato- 

mite, globigerina-ooze, lignite, miliolite. 
Mineral characters : aplite, diorite ; 

albitite, amphibolite, anorthosite, argillite, augitite, 

hornblendite, quartzite, peridotite ; 

albite-enstatite rock, anorthite rock, muscovite-rutile 

rock, quartz-barytes rock ; 

glauconitic sandstone, glaucophane-schist, hornblende- 
granite, mica-schist, nepheline-syenite, olivine-basalt, 

quartz-monzonite, sillimanite-gneiss. 
Chemical characters: alkali-rocks, anthracite, calc-alkali- 

rocks, calc-flinta, calciphyre, picrite, soda-rhyolite. 
Use : laterite, novaculite. 
Mode of formation : crush-breccia, flow-breccia, mylonite, 


Alteration : diabase, rapakivi. 
Relative age : palasopicrite, proterobase, protogine. 
Tribal names : gondite, ossypite. 
Surnames : buchnerite, charnockite, dolomite, grahamite. 

Place-names : cornubianite, ivernite, norite ; 

andesite, bostonite, canadite, jacupirangite, laurdalite, 

monchiquite, nevadite, sussexite, tonalite, wyomingite. 

Hunne diabase, Markle basalt, Ponza trachyte. 
Compound rock-names: granodiorite, rhyodacite, syeno. 

diorite, trachydolerite. 
Greek prefixes: apo-rhyolite, epidiorite, hyalobasalt, kata- 

gneiss, micropegmatite, orthogneiss, paragneiss, pseudo- 



Greek suffixes: basanitoid, dacitoid, graneid, pegmatoid, 

Mnemonics: felsic, femic, mafic, salic. 

For many years the fashion has been established 
of basing new rock-names on geographical names, 
a method that burdens the memory with many ugly 
and cacophonous terms, leads sometimes to re- 
dundancy, and fails to suggest the distinctive 
characters of the rock-types so described. It is 
difficult, however, to see how these objections can 
be altogether avoided. A different application of 
the method has sometimes been made, a new type 
being described partly in terms of a well-known 
rock-name, and partly in terms of the locality where 
the type-rock occurs. Thus we have Ponza 
trachyte, Hunne diabase, and Markle basalt. More 
purely descriptive names, formed by adding 
mineral-prefixes to existing rock-names, such as 
biotite-hornblende-granite, are self-explanatory; 
and the same advantage is shared by compound 
terms like granodiorite, trachyandesite, and melano. 
cratic olivine-trachydolerite. There is much to be 
said in favour of combinations of these kinds, as 
they reduce the number of fundamental names to be 
remembered, and are of wider application than 
specific names. Many protests have been made 
against the use of long compound-names, but, 
unless they become ridiculously cumbrous, they are 
thoroughly justified in the interests of clearness, as 
they are, for example, in organic chemistry. 

A geographical appellation already established, 
such as lugarite or marloesite, should not be 


adopted for a rock from a fresh locality, unless the 
identity of type so implied is sufficiently close to 
avoid all chance of misconception. On the other 
hand, a new name should not be resorted to until 
every other possibility has been tested and found 
inadequate. There is undoubtedly an attraction in 
the creation of new names, and in too many cases 
that attraction has not been dispelled by the verbal 
discords eventually produced. On several occa- 
sions in my own experience I have been inclined to 
coin specific names. A riebeckite-asgirine granite 
from Angola 1 was a temptation for a time, but fortu- 
nately it was resisted. Otherwise our nomencla- 
ture would have been burdened with two new and 
unnecessary synonyms, for simultaneously Lacroix 
described a similar rock from Madagascar 2 under 
the name fasibitikite. In a case like this I consider 
that three words are better than one. Brevity of 
expression is by no means an unmixed blessing, 
and the one word may require a whole paragraph of 

It would, of course, be desirable if definitions of 
rock-names could be framed by an International 
Committee endowed with authority to fix meanings 
finally, and to decide on the validity of new terms 
at suitable intervals. Unfortunately such a counsel 
of perfection is not likely to be sought for many 
years, and even were a powerful committee to be 
formed, its authority would sooner or later be 
sapped by disagreement. One such attempt to 

1 A. Holmes : Geol. Mag., 1915, p. 267. 

2 C.R., clxi, 1915, p. 253. 


standardise nomenclature revealed so wide and 
stubborn a divergency of opinion as to its prac- 
ticability, and the individual rights of authors to 
use terms as they choose, that no final decisions 
were arrived at, and only a few general suggestions 
and the revised Lexique of Lcewinson-Lessing 
emerged from the conferences. 1 The authors of 
the Quantitative Classification of Igneous Rocks 
have summed up the position by a quotation so 
happy that no apology is necessary for repeating it 

" There's glory for you," said Hnmpty Dumpty. 

" I don't know what you mean by glory," Alice said. 

Humpty Dumpty smiled contemptuously. " Of course you 
don't till I tell you. I meant there's a nice knock-down 
argument for you !" 

" But glory doesn't mean ' a nice knock-down argument,' " 
Alice objected. 

" When / use a word," Humpty Dumpty said in rather a 
scornful tone, " it means just what I choose it to mean 
neither more nor less." 

" The question is," said Alice, " whether you can make a 
word mean so many different things." 

" The question is," said Humpty Dumpty, " which is to be 
master that's all." 

Alice Through the Looking Glass (Lewis Carroll). 

Two main difficulties stand in the way of uni- 
versal agreement. One of these is the natural 
tendency of words in active use to grow, and 

1 Com-ptes Rendus, viii, Congres Geologique International, 
Paris (1900), 1901. 

2 W. Cross, J. P. Iddings, L. V. Pirsson, & H. S. Washing- 

ton : Journ. Geol., xx, 1912, p. 559. 


gradually to assume a wider and therefore less pre- 
cise meaning than that for which they were 
originally intended; while in time they may come 
to have a totally new, and at first sight quite un- 
related, meaning. The standard petrological 
example of a word illustrating this process is 
porphyry ; and quite recently the term dedolomitisa- 
tion began to extend its scope, though in this case 
the tendency was thwarted by a timely protest. 1 
Even in 1811 we find Pinkerton complaining in his 
Petralogy that the term freestone, instead of being 
restricted to "the noblest of the common lime- 
stones," had been inaccurately applied to sand- 
stones! He overcame this "abuse of language" 
by proposing konite for the limestones so beloved 
of the mediaeval freemasons. And introducing 
another rock which he describes with great 
enthusiasm, he writes, "This is the celebrated 
pudding-stone of England, so much in request in 
foreign countries; but this name commonly excit- 
ing a smile among the illiterate, and the applica- 
tion being since enlarged to a great number of 
glutenites, 2 of a different nature and origin, form- 
ing entire chains of mountains (while this is con- 
fined to a very small district in England, and is 
found nowhere else in the world), it has been 
thought proper to distinguish it by the name of 
Kollanite; derived from the Greek, denoting its 
appearance of being cemented together." 

1 Geol. Mag., 1919, p. 458. 

2 A term, mow obsolete, for breccias, conglomerates, and 



The late A. D. Darbishire in his posthumous and 
unfinished Introduction to a Biology (1917) dis- 
cussed the wanderings of words in relation to a 
subject where the danger is even greater than in 

" If there is a possibility that words give a 
semblance of progress in interpretation, where in 
reality there is none, it is desirable that some atten- 
tion should be paid to the relation between word 
and thought. . . . 

" A word and its meaning, especially in the case 
of ideas, are united together by a slender, elastic 
bond which is now contracted, now stretched to its 
uttermost. ... So we see the word and its mean- 
ing dancing to each other in an airy medium, like a 
pair of gnats in the lee of a gorse-bush. This, 
alas ! is the simplest case. The more complicated 
and much more common cases are those in which 
one word has more than one meaning, or where one 
meaning has more than one word to express it; 
these are the cases which, in verbal life, are pro- 
ductive of trouble " (pp. 19-21). 

Such difficulties are sometimes accentuated by 
human perversity : witness Rosenbusch's treat- 
ment of Vogelsang's term granophyre, and 
Brogger's appropriation of foyaite and ditroite. 
Consider also the introduction of the terms aa and 
aphrolith to denote the qualities already simply ex- 
pressed by block-lava-, and of midalkalite and 
syenoid to take the place of nepheline-syenite. 

The second difficulty standing in the way of 
agreement is intimately related to the first. 


Although petrology is now developing rapidly, no 
generally accepted classifications of the major 
groups of rocks have yet been devised with suffi- 
cient detail to guide the choice of terminology and 
to restrain its tendency to spread outwards and be- 
come confused. Existing classifications involve a 
and chemical composition, proportions of minerals, 
and chemical composition, proportions of minerals, 
structure, texture, mode of occurrence, degree of 
alteration, etc. and any given name is therefore 
liable to wander in various directions according as 
insistence is placed on one or other of its possible 
connotations. A successful classification will need 
to be sufficiently elastic to avoid the despotism of 
merely arbitrary and unsignificant division, and 
yet sufficiently rigid to standardise the meanings of 
its collateral terminology. 

At the present time the field of petrology still 
contains many uncultivated corners, and until the 
whole has become familiar ground, existing 
systems of classification and nomenclature must be 
regarded as on probation. It is my impression that 
stability will be approached, not primarily as a 
result of any committee, international or sectional, 
but by the co-ordinating work of a single petrolo- 
gist of genius whose authority, the outcome of his 
own success and influence, will be far superior to 
the merely temporising and democratic authority 
of a committee. 

Meanwhile it seems desirable to take stock, and 
to place on record the existing nomenclature in 
accordance with its current usage. It is hoped that 


this book will meet the need by creating a standard 
of reference which may to some extent limit future 
vacillations, and prevent unnecessary clashing 
between new terms. The main object of the book 
is, however, to be practically useful by serving as a 
guide to student, teacher, research-worker, and 
professional geologist, and indeed to all who need 
to follow petrological literature or to contribute to 
its pages. 

The work involved in revising and amplifying 
the original card-catalogue, undertaken about a 
year ago, proved to be more arduous than 
was at first anticipated. It has, however, never 
descended to drudgery or mere compilation. On 
the contrary it has been in the nature of a literary 
exploration, leading one to examine a century's 
evolution of petrological thought and method, and 
to share the delights of many a curious traveller 
through little-known corners of lands the world 
over. Unsatisfactory though certain parts of the 
nomenclature may be as an instrument of thought 
and exposition, it is, as a w^hole, unusually rich in 
pleasant associations, geographical, historical, and 
even psychological. Perhaps this romantic aspect 
of a subject bristling with technicalities is a dan- 
gerous one, for it tends to support the natural con- 
servatism of even scientific men, and so, perhaps, 
to retard the development of that ideal system of 
nomenclature which we all hope for but cannot as 
yet create. 

Certain attempts to systematise nomenclature 
have already been made, particularly in the field of 


igneous rocks. It is desirable to draw attention to 
some of these, because, with a few exceptions, the 
terms they comprise have been excluded from the 
glossary that follows. 

Jevons suggested a wholesale use of prefixes con- 
sisting of contracted, or rather mutilated, forms of 
structural, textural, and mineral names, together 
with a few chemical and qualifying syllables. 1 He 
thus arrived at such combinations as ophit-oli- 
dolerite, diopsi-mipegmo-rhyolite, rhomfels-pyr- 
alisyenite ( = Laurvikite), and eud&gi-midalkalite 
( = Lujaurite). Such proposals are obviously fore- 
doomed to failure. In the words of Professor 
Bonney, "Time is not so valuable, or paper and 
printing so expensive, that we should talk or write 
4 gibberish ' to save a few letters." 

A more reasonable method has recently been 
proppsed by Professor Shand, 2 based in its applica- 
tion on the classification of igneous rocks according 
to his principle of saturation. 3 He suggests 

(1) That the names of oversaturated and saturated 
rocks should end in the customary suffix -He ; e.g., 
granite, syenite, etc.; 

(2) That the names of unsaturated rocks should 

(a) the prefix sub-, or the suffix -ole, to indicate 
that the dyad or triad metals are unsaturated ; 
e.g., subgabbro, for olivine-gabbro ; 

(b) the suffix -oid, to indicate that the monad 

1 H. S. Jevons : GeoL Mag., 1901, p. 304. 

2 S. J. Shand : Geol. Mag., 1917, p. 466. 

3 GeoL Mag., 1913, p. 508; 1914, p. 485; 1917, p. 115. 


metals are unsaturated; e.g., syenoid, for 
nepheline-syenite ; and 

(c) a combination of the prefix sub- and the 
suffix -old, to indicate that both monad and 
dyad metals are unsaturated, e.g., subthera- 
loid or subgabbroid, for olivine-theralite. 
The principle adopted is excellent, but the choice 
of suffix, -aid, is unfortunate and cannot be 
accepted, for it has already been seriously over- 
worked in other directions. It has been used in 
adjectival terms like granitoid and trachytoid, tc- 
express texture or composition ; and in substantive 
form in the term pegmatoid, to denote very coarse- 
grained facies of igneous rocks differing from peg- 
matite proper by the absence of graphic-texture; 
and in terms of which dacitoid is a typical example, 
to connote similarity (to dacite) of chemical com- 
position combined with dissimilarity of mineral 

The authors of the Quantitative Classification 
have introduced a very comprehensive nomencla- 
ture, the greater part of which is built up with the 
aid of a variety of suffixes and mnemonic contrac- 
tions. Terms like felsic and mafic are extremely 
useful, and even though they have been regarded 
as technical slang, they have justified their inven- 
tion by having been widely adopted. On the other 
hand, more ambitious and less useful terms such as 
alferfemphyric are ugly and have not met with a 
similar measure of favour. Cross, Iddings, 
Pirsson and Washington 1 have themselves made 

1 These authors are referred to in the glossary by CJ.P.W, 


the recognition of much of their nomenclature a 
necessity, for they have forcibly and persistently 
made use of it in a long series of publications which 
other petrologists cannot afford to ignore. Most of 
the new terminology, however, is intimately related 
to, and only used in connection with, the Classifica- 
tion itself, and with the latter it must therefore stand 
or fall. Unfortunately, the principles on which the 
Classification is based leave the main problems of 
petrology untouched, fail to open out new fields of 
research, and therefore do not constitute a creative 
contribution to the subject they were intended to 
illuminate. From this point of view the apparently 
wide influence exerted by the Classification in 
recent years has been largely factitious. Neverthe- 
less, it is only fair to add that the authors of the 
Classification have rendered very real services to 
petrology by promoting greater accuracy of 
description and analysis, and by introducing the 
conception of the norm, which provides an admir- 
able method of recalculating, comparing, and inter- 
preting rock-analyses. 

Another systematic terminology to which refer- 
ence must be made has he_en proposed and exten- 
sively used by Grabau in his Principles of Strati- 
graphy (1913). The terms are summarised on 
pp. 296-7 of that work, and constitute an attempt, 
laudable in principle, to provide a comprehensive 
nomenclature for sedimentary and associated rocks. 
By means of a number of prefixes representing 
chemical or mineral composition and agency of 
formation, compound terms are built up at will by 


combining them with a series of grade designa- 
tions : rudyte, corresponding to gravel, shingle, 
pebbles, etc.; ar&nyte, corresponding to sand; and 
lutyte, corresponding to mud or rock-flour. Thus 
anemoarenyte in ordinary terms would be described 
as asolian sand; hydrosilicirudyte as quartz-con- 
glomerate; and pyrolutyte as volcanic ash or 
dust. The extent of departure from current 
nomenclature is unnecessarily wide, and it seems 
doubtful whether such innovations will ever be 
recognised by adoption. Grabau's use of the terms 
exogenetic and endogenetic is particularly unfortu- 
nate and tends to confusion of thought. 1 He 
describes rocks as "exogenetic" when they have 
been formed by agents acting from without, that is, 
acting externally with respect to, and indepen- 
dently of, the finished rock, as in the case of loose 
detrital sediments. Other rocks, formed by agents 
acting from within, he describes as "endogenetic," 
this category including igneous rocks, saline 
deposits, and organic accumulations. The two 
contrasting terms, although they are applied to 
rocks, are thus made to be synonymous with 
allo genie and authigenic respectively, and as the 
latter terms lead to a far clearer realisation of the 
primary division proposed by Grabau there seems 
to be no reason for rejecting them. The sentence 
" A calcareous sandstone contains allogenic grains 
held together by an authigenic cement," gives an 
accurate statement of fact, whereas the classifica- 

1 Amer, Geol., xxxiii, 1904, p. 228, 


tion of a calcareous sandstone as " exogenetic " in 
Grabau's sense expresses only part of the truth. 

The obvious and most serviceable meanings of 
exogenetic and endogenetic are those proposed by 
Mr. T. Crook, 1 and they should be adopted and 
used as defined by him. Exogenetic applies 
to processes originating and operating at or near 
the earth's surface, and to the rocks and ore- 
deposits formed by such processes. Endogenetic 
applies to processes originating internally and 
operating deep-seatedly in the earth's crust, or from 
within outwards, and to the rocks and ore-deposits 
formed by such processes. 

If it be objected that Grabau has priority as re- 
gards date of publication, the reasons for rejecting 
his usage would be based on the following points 

(a) The French equivalents of the terms, 
exogene and endogene, have long been used 
to express the division of rocks into ' * erup- 
tive " and " sedimentary " groups. 

(b) Reference to Murray's Oxford Dictionary 
will show that exogenetic had previously 
been recognised in the sense followed by 

(c) Grabau has used the terms for a concep- 
tion which they fail adequately to express, 
and for which wholly adequate terms were 
already available. 

Only one of Grabau's terms, rudaceous, has been 
included in the glossary, because with arenaceous 

1 " The genetic classification of rocks and ore deposits,'' 
Min. Mag. t xvii, 1914, p. 72. 


and argillaceous, it completes a Latin trilogy for 
the three main groups of detrital sediments. As 
far as I know there has not hitherto been a term of 
Latin form for coarsely graded detritus of the kind 
which is described in the corresponding Greek 
trilogy as Psephitic. 

Several of the Cross-Iddings-Pirsson-Washing- 
ton terms have been incorporated, including a 
selection of the chief key-words and prefixes of the 
nomenclature associated with the divisions of the 
classification . The greater part of that terminology 
has been excluded, and those wishing to become 
familiar with its details are referred to the various 
publications cited below. 1 

In addition to the excluded terms already referred 
to, certain others have also been omitted : 

(a) Modifications of existing terms such as 
Johannsen's 2 field terms, graneid, dolereid, 
anameseid porphyry, etc.; and Dana's 3 and 
Graubau's 4 terms ending in -yte instead of 
-lie . 

(b) Most compound terms built up from 
mineral qualifiers. These are, of course, in- 

1 C.I.P.W. : Journ. GeoL, x, 1902, pp. 555-690. 

Quantitative Classification of Igneous Rocks, Chicago, 

1903. (Glossary on pp. 261-284.) 
J. P. Iddings : Igneous Rocks, I, 1909, pp. 394-454. 
C.I.P.W. : Journ. GeoL, xx, 1912, pp. 550-561. 
G. I. F inlay : Introduction to the Study of Igneous Rocks, 

1913, pp. 143-221. 
H. S. Washington : Chemical Analyses of Igneous Rocks 

(U.S.G.S. Prof. Pap., 99). 1917, pp. 1151-1161. 

2 A. Johannsen : Journ. Geol., xix, ign, p. 317. 

3 J. D. Dana : Am. Journ. Sci. and Art, xvi, 1879, p. 336. 

4 A. W. Grabau : Principles of Stratigraphy, 1913, p. 298. 


numerable and would unnecessarily over- 
burden the glossary. 1 Where the qualifier 
has become an essential part of the name of 
an important group of rocks, as in quartz- 
diorite, nepheline-syenite, chlorite-schist, 
etc., the resulting term has, however, been 

(c) Most obsolete terms, such as those proposed 
by Pinkerton in his Petrology. Two of 
these, konite and kollanile, have already been 
mentioned. A few terms that have more 
recently fallen into desuetude are introduced, 
partly to indicate the reason for their obsoles- 
cence and partly because they may be met 
with in literature that has not yet been super- 

With these exceptions the glossary forming the 
greater part of this book is believed to be reason- 
ably complete. The general treatment is his- 
torical rather than critical, the main object 
being to record the customary current mean- 
ing of each term, together with the original 
author and the date of its first use, and 
in the case of rock-names the type-locality. It has 
been no part of my purpose either to recommend or 
discourage the use of any recognised term, and 
throughout I have abstained from discussing either 
the value of a term, or the need for it. A critical 
examination of terminology could be conducted 
more satisfactorily from the standpoint of classifica- 

1 See also J. D. Dana : Am. Journ. Sci., xxxii, 1886, p. 71. 


As will be seen from the glossary itself, the terms 
incorporated include not only those describing 
rocks, structural and textural features, modes of 
occurrence, and processes, but also a selection of 
terms associated with petrographic methods, most 
terms referring to crystal optics and physics 
being excluded. In the case of terms denoting the 
mode of occurrence of igneous rocks (e.g. batholith) 
it seemed desirable to introduce a uniform ending 
-lith throughout. Thus, instead of Gilbert's lacco- 
lite and Marker's phacolite, the forms laccolith and 
phacolith have been adopted. This course serves 
to distinguish such names from mineral and rock 
names, and in the case of phacolith it avoids 
possible confusion with the zeolite phacolite. Dr. 
Harker, who has hitherto used the ending -ite, 
raises no active objection to the change suggested. 

In the case of the mineral names cegirine, 
nepheline, nosean, hauyne, the form of spelling 
here given has been retained, but analcime has 
been allowed to yield to analcite. The original and 
more harmonious termination was given by Haiiy 
in 1801, but the more systematic ending adopted 
by Galitzin, also in 1801, seems to have achieved 
greater currency. Moreover, the latter form has 
been fixed by the rock-name analcitite, whereas it 
is nepheline and not nephelite that is fixed by the 
corresponding rock-name nephelinite. 

Selected references to the literature of the respec- 
tive subjects have been appended to many of the 
items of the glossary. The choice of reference has 
not always been easy. It is manifestly impossible 


to give a complete series of references in the case 
of the older terms, and to give the original refer- 
ences alone is neither desirable nor necessary, as 
they are already available in Lcewinson-Lessing's 
Lexique. The guiding principle has been to draw 
attention to recent and readily accessible papers 
which in turn serve to open out the older literature. 
Had it been followed rigidly this course would have 
led to the exclusion of many of the important papers 
which we owe to the pioneers and veterans of petro- 
logical research, and it would then have appeared 
that the authors alluded to had been unduly 
neglected. For this reason occasional references to 
the older papers have been inserted in appropriate 

For the literature dealing with the igneous 
geology of particular districts the second part of 
Iddings' Igneous Rocks, Vol. II., is the most 
accessible source; while for individual rock-types 
the copious references given in Washington's tables 
of chemical analyses 1 cover the whole field up to 

Appendices giving French and German words 
have been added as a help to students reading petro- 
logical literature in these languages. 2 Terms of 
an international character, and words which are 
readily recognised by their similarity to the Eng- 

1 U.S.G.S., Prof. Pa-p. 99, 1917. 

2 A useful dictionary for scientific purposes is A German- 

English Dictionary for Chemists, by A. M. Patterson, 
1917, as it contains an ample general vocabulary in addi- 
tion to the technical terms of chemistry and related 


lish equivalents have been omitted. The German 
appendix has been compiled by Miss J. H. Robert- 
son, for whose help I wish here to acknowledge my 
gratitude. Appendices setting forth Greek and 
Latin words have also been added in order to make 
clear the significance of the many petrographical 
and mineralogical terms into which they enter. 

Classification Tables have been introduced in 
order to bring together terms representing closely 
related concepts. These will be found useful not 
only in taking a broad survey of certain parts of the 
subject, but also in serving as a guide to new or for- 
gotten terms. The tables also bring out the 
" patchiness " of petrological nomenclature. Cer- 
tain parts of the subject are heavily burdened with 
redundant terms, and with others that depend for 
their justification on differences so slight or trivial 
that they have but little practical value. Other 
parts of the subject, particularly those involv- 
ing altered and metamorphic rocks have still a 
somewhat restricted nomenclature. This is prob- 
ably due to the fact that until recent years attention 
had been focussed almost exclusively on igneous 
rocks, with the result that petrology has developed 
somewhat unequally. Fortunately the outlook is 
gradually widening, and even ore-deposits and 
meteorites are beginning to take a recognised place 
in the subject to which they properly belong. 

In the hope of making the glossary as representa- 
tive as possible of customary modern usage, twenty 
preliminary proofs were pulled and sent to various 


petrologists with a view to eliciting sugges- 
tions, comments, and constructive criticism. This 
plan proved highly successful, and a very valuable 
series of replies was received from the following 
gentlemen : Prof. T. G. Bonney, Prof. P. G. H. 
Boswell, Mr. Alfred Brammall, Prof. Grenville A. 
J. Cole, Prof. A. Hubert Cox, Mr. T. Crook, Dr. 
J. V. Elsden, Dr. J. W. Evans, Mr. J. F. N. 
Green, Dr. A. Harker, Dr. W. R. Jones, Prof. A. 
Lacroix, Dr. G. T. Prior, Prof. P. Quensel, Mr. 
W. Campbell Smith, Sir Jethro Teall, Dr. H. H. 
Thomas, Mr. G. W. Tyrrell and Prof. W. W. 
Watts. To all these I owe my heartiest thanks for 
their very substantial help in bringing to com- 
pletion my self-appointed task. As a result of 
their approval of the project itself, and their active 
assistance in suggesting additions and modifica- 
tions, I am supported in my belief that the book 
will meet a real need, and encouraged in my hope 
that the design originally conceived may have been 
brought to a successful issue. 

Finally, I wish to invite the further aid of those 
who use the glossary, by asking them to acquaint 
me with the particulars of any errors of interpreta- 
tion or reference that may be detected, and to sug- 
gest any additional terms that have unwittingly 
been overlooked. Should the opportunity arise, 
such corrections will be incorporated in a revised 
edition, and as the "completion" of a glossary 
such as this is necessarily relative to the date of 
publication, authors of new terms are invited to 


ensure their future inclusion by communicating 
with me either directly, or, if necessary, through 
the publishers. 


Imperial College of Science and Technology, 
South Kensington, S.W.7, 
January, 1920. 



Aa, Dutton, 1883. A Hawaian term for block-lava, 
consisting generally of a rough tumultuous assem- 
blage of clinker-like scoriaceous masses. =Aphro- 
lithic lava. Cf. Pahoehoe. 

R. A. Daly : Igneous Rocks and their Origin, 1914, p. 291. 
J. A. Jaggar : Journ. W ash. Acad. Sci., vii, 1917. 
Aasby Diabase, Tornebohm, 1877. A type of olivine- 
dolerite containing biotite, ilmenite, and apatite, 
in addition to'labradorite, augite and olivine. 

(Aasby, Sweden.) 

Absarokite, ladings, 1895. A porphyritic, basaltic or 
trachy-doleritic rock, characterised by the presence 
of phenocrysts of olivine, augite, and labradorite 
in a base containing orthoclase-mantled labra- 
dorite. (Absaroka Range, Yellowstone Park.) 
J. P. Iddings: Journ. GeoL, iii, 1895, p. 938. 
U.S.G.S., Mon., xxxii (ii), 1899, p. 328. 

Abyssal Assimilation, Daly. See Assimilation. 

Abyssal Injection, Daly, 1906. The process whereby 
magmas originating at considerable depths are 
considered to have been driven up through deep- 
seated contraction-fissures in the earth's crust. 
R. A. Daly : Igneous Rocks and their Origin, 1914, p. 174. 
Abyssal Rocks, Brogger. A general term for rocks 

of major intrusions. Cf. Plutonic. 

Accessory. A term applied to minerals occurring in 
small quantities in a rock, and whose presence 
or absence does not affect its diagnosis. 
R. H. Rastall & W. H. Wilcockson : QJ.G.S., Ixxi, 1915, 

p. 592. 
P. G. H. Boswell: GeoL Mag., 1916, p. 165. 


Accidental Inclusions, Harker, 1900. A term applied 
to xenocrysts or xenoliths having no genetic con- 
nection with the igneous rocks in which they oc- 
cur ; = enclaves enallo genes. 
A. Harker: Journ. GeoL, viii, 1900, p. 389. 

Achondrite, Cohen. A general term for stony meteo- 
rites (aerolites) free from the spheroidal structures 
known as chondrules. Cf. Chondrite. 

Acid- A term applied to igneous rocks having a 
higher percentage of silica than orthoclase, the 
limiting figure commonly adopted being 66 per 
cent. Cf. Persilicic and Over saturated. 

Adamellite, Cathrein, 1890. A term applied origin- 
ally to an orthoclase-bearing tonalite, and now 
used generally for granites in which plagioclase 
varies from one-third to two-thirds of the total 
felspar. = Quartz-monzonite. 

(Mt. Adamello, Tyrol.) 
W. C. Brogger : Eru-ptivgesl. Kristiania, ii, 1895, p. 61. 

Adinole, Haus smarm, 1847. A contact modification 
of shale or slate metamorphosed and albitised by 
doleritic (albite-diabase) intrusions ; consists of a 
mosaic of albite, or albite and quartz, with inter- 
stitial chlorite and iron-ores. 
H. Dewey : Trans. Roy. Geol. Soc. Cornwall, xv, 1915, p. 71. 

Adobe, Russell, 1889. A loess-like deposit occurring 
in the plains and basins of the Western States, and 
in the arid parts of Spanish America. 

Adsorption. A term applied to the change in con- 
centration of solutions and colloids where they 
come into contact with surfaces. 

Aeolian. A term applied to deposits whose constit- 
uents have been carried by, and laid down from, 
the wind. 

S. C. Stuntz & E. E. Free : U.S.A. De-pt. Agriculture, Bureau 
of Soils, Butt. 68. 

Aerolite. A general term for meteoric stones, that is 
for meteorites composed mainly of silicates such as 
pyroxenes and olivine, with or without small quan- 
tities of nickel-iron, troilite, etc. According as 


chondrules are present or absent, aerolites are 
divided into chondrites and achondrites (q-v.). 

Agglomerate, Lyell, 1831. A chaotic assemblage of 
coarse angular pyroclastic materials. 

Aggregate Polarisation. The mottled appearance 
seen between crossed nicols of a mineral aggregate 
composed of minute particles which are orientated 

Agpaite, Ussing, 1911. A general term applied to the 
felspathoidal rocks of Ilimansak, Greenland, and 
including sodalite-foyaite, naujaite, lujaurite, and 

N. V. Ussing : Medd. om. Grdnland, xxxviii, 1911. 
Jlsyte, Heddle, 1897. A variety of riebeckite micro- 
granite, or paisanite. (Ailsa Craig.) 

. 1. J. H. Teall : Min. Mag., ix, 1891, p. 219. 
.kerite, Broggcr, 1890. A variety of quartziferous 
augite-syenite, containing soda-microcline and 
oligoclase. (Aker, Norway.) 

W. C. Brogger : Eru-ptivgest. Kristiania, ii, 1895, p. 43. 

Alaskite, Spurr, 1900. A leucocratic granite, contain- 
ing quartz and alkali-felspars, with only traces of 
other minerals. (Alaska.) 

J. E. Spurr : Amer. GeoL, xxv, 1900, p. 231. 

Hlbertite, How, 1860. A black variety of bitumen 
with a brilliant lustre and conchoidal fracture. 
H = i 2 ; S.G. about i.i. It differs from manjak 
and uintaite by being practically insoluble in alco- 
hol, and only partly so in turpentine. 

(Albert Mines, New Brunswick.) 

Albite-diabase. An altered and albitised doleritic 
rock, containing albite in place of the usual plagio- 
clase ; purple brown augite more or less replaced 
by epidote, chlorite, and calcite, and titaniferous 
magnetite ; the intrusive equivalent of spilite. 
H. Dewey & J. S. Flett : GeoL Mag., 1911, p. 202. 

Albite-enstatite Rock, Els den, 1905. A local fades, 
possibly aplitic, of the enstatite-diorite of Pen- 
clegyr. (Forth Gain, Pembroke.) 

J. V. Elsden : Q.J.G.S., Ixi, 1905, p. 579. 


Albitisation. The process, due to paulopost juvenile 
action, whereby the plagioclase (originally richer 
in anorthite) of igneous rocks is replaced by albite ; 
e.g., in spilite. 

E. B. Bailey & G. W. Grabham : Geol. Mag., 1909, p. 250 
H. Dewey & J. S. Flett : Geol. Mag., 1911, p. 202. 
N. Sundius : Geol. For. i Stockholm Fork., xxxiv, 1912, 

P- 3 1 ?- 
Albitite, Turner, 1896. A leucocratic soda-syenite or 

porphyry composed almost wholly of albite. 
H. W. Turner : U.S.G.S. i^th Ann. Rep., ii, 1896, p. 477, 
Albitophyre, Coquand, 1857. A porphyry in which 
the felspar phenocrysts and the microlites of .he 
groundmass are chiefly albite. Cf. Orthophyre. ^_ 
A. Holmes : Geol. Mag., 1917, p. 403. 

Alboranite, Becke, 1899. A variety of ' ' hypersthenv 
andesite," containing plagioclase at least as cal^ifl 
as labradorite ; i.e., hypersthene-basalt with 
microlitic texture like that of an andesite. \ 

(Alboran Is., Spain.' 

Aleutite, Spurr, 1900. A term suggested for porphy- 

ritic varieties of belugite (rocks intermediate 

between diorite and gabbro) having an aphanitic or 

finely crystalline groundmass. (Aleutian Is.) 

J. E. Spurr : U.S.G.S., 2oth Ann. Re-p., Pt. vii, 1900, p. 195. 

Algovite, W inkier, 1859. A group-term for a series of 

augite-plagioclase rocks ranging from dolerite 

through porphyritic varieties to gabbro. 

(Algauer Alps.) 

Alkali Rocks. -- Igneous rocks in which the abund- 
ance of alkalies in relation to other constituents 
has impressed a distinctive mineralogical char- 
acter ; generally indicated by the presence of soda 
pyroxenes, soda amphiboles, and/or felspathoids. 
Cf. Calc-alkali Rocks. 

A. Lacroix : Nouv. Arch. Mus. cVHist. Nat., iv, 1902, p. 178. 
G. T. Prior : Min. Mag., xiii, 1903, p. 254. 
A. Harker : Nat. Hist. 1 g. Rocks, 1909, p. 90. 
N. L. Bowen : Journ. Geol., Supp. to xxiii, 1915, p. 55. 
A. Holmes : Q.J.G.S., Ixxii, 1916, pp. 268, 272. 
R. A. Daly : Journ. Geol., xxvi, 1918, p. 97. 


Allalinite, Rosenbusch, 1895. A term applied to com- 
pletely altered gabbros, the secondary minerals of 
which smarag-dite, actinolite, and saussuritic 
aggregates still occur as idiomorphic pseudo- 
morphs after the original minerals, the initial tex- 
ture of the rock being- thus retained. Contrasted 
with flaser-gabbro, in which metamorphism has in- 
volved structural as well as mineralogical changes. 

(Allalin, near Zermatt.) 

Allivalite, Harker, 1908. A phanerocrystalline rock, 
consisting of anorthite and olivine in approxi- 
mately equal proportions, or with felspar pre- 
ponderating-. (Allival, Rum.) 
A. Harker : Mem. Geol. Surv. Scot., 60 (Small Isles), 1908, 
P. 71- 

Allochetite, Ippen, 1903. - - A microlitic dyke rock 
with phenocrysts of labradorite, orthoclase, nephe- 
line and augite in a groundmass of felsic minerals 
with augite and hornblende. (Allochet, Monzonj.) 
J. A. Tppen : Verliandl. d. K.K. Geol. Rcichs., Wien, 1903, 
p. 132. 

Allochthonous, G umbel, 1888. - - A term applied to 
rocks of which the dominant constituents have not 
been formed in situ. Cf. Autochthonous. 

Allothigenous, or AHogenic, Kalkovsky, 1880. 

Terms, meaning- generated elsewhere, applied 
to those constituents that came into existence out- 
side of, and previously to, the rock of which they 
now constitute a part; e.g., the pebbles of a con- 
glomerate. Cf. Authigenous. 

Allotriornorphic, Rosenbusch, 1887. A term applied 
to those minerals of igneous rocks which are not 
bounded by their characteristic crystal faces. = 
Anhedral = Xenomorphic. 

AHotropy. A term denoting the capacity of an 
element to exist in more than one form while in 
the same state; e.g., graphite and diamond, 
orthorhombic and monoclinic sulphur, oxygen and 



A similar phenomenon is exhibited by many 
compounds, und is then generally known as 
dimorphism or polymorphism, though the term 
allotropy has also been extended to cover such 
cases, e.g. , the a, j8, and 7 forms of zircon, readily 
distinguished by their specific gravities. 

For a discussion of allotropy in relation to rock magmas 
see W. H. Goodchild, Mining Mag., xviii, 1918, p. 243. 
Alluvium. A general term for all detrital deposits "re- 
sulting from the operations of modern rivers, thus 
including the sediments laid down in river-beds, 
flood-plains, lakes, fans at the foot of mountain 
slopes, and estuaries. 

Alphitite, Salomon, 1915. A term suggested for clays 
consisting largely of rock-flour, such as those 
washed and laid down from glacial debris. 
W. Salomon : Geol. Rund., vi, 1915, p. 398. 
Alnoite, Rosenbusch, 1887. A dyke-rock, containing 
phenocrysts of biotite, olivine and augite in a 
groundmass composed of melilite and augite, w'ith 
sometimes perovskite, and other accessories. By 
increase of melilite alnoite passes into melilite- 
basalt. (Alno, Sweden.} 

F. D. Adams : Ajit. Journ. Sci., xliii, 1892, p. 269. 
J. S. Flett : Trans. Roy. Soc. Edin., xxxix, 1900, p. 891. 
Alsbachite, Chelius, 1892. A porphyritic variety of 
aplite, sometimes containing garnet. 

(Alsbach, Odenwald.) 

Alum-shale. -- A shale impregnated with alum, the 
latter constituent being due to the action on 
sericite of sulphuric acid produced by the oxida- 
tion and hydration of pyrite. 

Ambonite, Verbeck, 1905. A variety of hornblende- 

biotite-andesite characterised by the presence of 

cordierite. (Ambon Is., Moluccas.) 

Amherstite, Watson & Taber, 1913. -- A variety of 

syenodiorite containing andesine-antiperthite. 

(Amherst Co., Virginia.) 
T. L. Watson & S. Taber : Geol. Snrv. Virginia, Bull. 3 A, 


Amorphous. A term applied to substances which are 
not known to possess the discontinuous vector! al 
properties or the periodic arrangement of com- 
ponent atoms that characterise the crystalline 
A. F. Rogers : Journ. GeoL, xxv, 1917, p. 515. 

Ampelite. A general term for black bituminous or 
carbonaceous shales, often pyritic. 

Amphibole-magnetite Rock. A granulose often 

banded rock containing- grunerite and other fer- 
ruginous silicates, and magnetite, produced by the 
contact metamorphism of ferruginous cherts 
(taconite, jaspillite, etc.). 

C. R. Van Rise C. K. Leith : U.S.G.S., Mon., Hi, 1911, 

PP- 55. 55 8 - 

Amphibolite, Brongniart, 1827. A granulose or 
glomero-blastic metamorphic rock, consisting 
essentially of amphibole and plagioclase, and 
often containing quartz, epidote, or garnet. 

G. A. J. Cole : Trans. Roy. Irish Ac ad., xxxi, 1900, p. 460. 

J. J. H. Teall : Mem. GeoL Surv. (N.W. Highlands), 1907, 

P. 5 6 - 

F. D. Adams : Journ. GeoL, xvii, 1909, p. i. 
P. Eskola : Bull. Comm. GeoL Finlande, No. 40, p. 97. 
A. Holmes : Q.J.G.S., Ixxiv, 1918, p. 58. 

F. L. Stillwell : Aust. Ant. Ex-ped. Sci. Rep. A, iii, I (i), 
(Met. Rocks, Adelie Land), 1918, p. 24, etc. 

Amphibololite, Lacroix, 1894. A general designation 
for phanerocrystalline igneous rocks entirely or 
almost entirely composed of amphiboles. 

A. Lacroix : Now. Arch, du Mits. d'Hist. Nat., vi, 1894, p. 

Amphoterite, Tschermak, 1683. -- An achondritic 
meteorite composed essentially of bronzite and 
olivine, with small amounts of oligoclase and iron 
rich in nickel. 

Amygdales or Amygdules. -- Vesicles or vapour 
cavities of volcanic and occasionally of intrusive 
rocks, which have become filled with secretionary 
products (usually of late-magmatic origin), such as 
zeolites, chlorite, forms of silica and calcite. The 


form amygdule is a diminutive of amygd&le, and 
consequently the former is not strictly synonymous 
with the latter. 
W. F. P. McLintock : Trans. Roy. Soc. Edin., li, Pt. i, 

iQi.5, P. T 3- 
A. Holmes : Q.J.G.S., Ixxii, 1916, p. 251. 

Amygdaloid. A general group-name for those vol- 
canic rocks (andesites, basalts, etc.) which are 
characterised by the presence of conspicuous 

Amygdaloidal. A term applied to rocks containing 
amvgdales, and to the structure resulting- from 
their presence. 

Anabohitsite, Lacroix, 1914. A variety of olivine- 
pyroxenite, containing- hypersthene and horn- 
blende, with a high proportion of magnetite and/ 
or ilmenite. (Anabohitsy, Madagascar.) 

A. Lacroix : C.R., clix, 1914, p. 419. 

Analcite-basalt, Lindgren, 1890. An olivine-bearing 
basaltic rock, in which the predominant felsic 
mineral is analcite ; felspar, if present, being 
merely accessory. Cf. leucite -basalt and rteph- 
H. S. Washington : Journ. Geol., xvii, 1914, P- 742. 

Analcite-dolerite. A dolerite, containing- analcite, 
usually as an interstitial constituent. The term is 
often used synonymously with Teschenite, but it 
is preferable to employ the latter term only for 
varieties containing- soda-pyroxenes and/or soda- 
amphiboles. Cf. Crinanite. 

Analcitisation, Flett, . 1900. - - The replacement of 
felspars or felspathoids by analcite by late or post- 
magmatic processes. 
A. Scott : Trans. Geol. Soc. Glasgow, xvi, 1915-6, p. 34. 

Analcitite, Pirsson, 1896. A term applied to rocks 
which differ from analcite-basalt only by the 
absence of olivine. Cf. leucitite and nephelinite. 

Anamesite, Leorihard, 1832. A term meaning- inter- 
mediate, applied to basaltic rocks that are of 
coarser grain than aphanitic basalts, and of finer 


grain than those dolerites in which the individual 
minerals can be megascopically distinguished. 
Anamorphism, Van Hise f 1904. - - The constructive 
metamorphism of rocks, characterised by the 
formation of complex minerals at the expense of 
simpler ones. 

C. R. Van Hise : U.S.G.S. Mon. 47, 1904. 

C. K. Leith & W. T. Mead : Metamor-phic Geology, 1915. 
Anatexis, Sederholm, 1907. --An ultrametamorphic 
process in which deep-seated rocks are remelted 
by the emanation of heat and hot gases from 
below, thus providing regenerated magmas in 
situ. Cf. Syntexis. 

J. J. Sederholm : Bull. Comm. Geol. Finlande, 23, 1907, 
p. 102. 
Cong. Geol. Inter. C.R. xii (1913), 1914, p. 319. 

P. J. Holmquist : Bull. Geol. Inst. Upsala, 15, 1916, p. 141. 

Anchi-etttectic, Vogt, 1905. A term applied to those 
rocks which are composed almost wholly of two or 
more minerals in nearly eutectic proportions. 
J. H. L. Vogt : References as below. 

Anchi-monomineralic, Vogt, 1905. A term applied 

to those rocks which are composed almost wholly 
of one kind of mineral; e.g., anorthosite, bron- 
zitite, congressite, dunite, etc. 

J. H. L. Vogt: Norsk Geol. Tidsskrijt, i, No. 2, 1905: 
Vidensk. Selsk. Skrift. Math- nat Klasse, No. 10, 1908. 

Anchorite, Lapworth, 1898. A nodular and veined 
variety of diorite, the normal fades of the rock 
being variegated with dark mafic segregation 
patches and light felsic contemporaneous veins. 

(Anchor Inn, near Caldecote, Nuneaton.) 

C. Lapworth : Proc. Geol. Assoc., xv, 1898, p. 419. 

Anden-diorite, Stelzner, 1885. A variety of quartz- 

iferous diorite having augite as its principal mafic 

mineral. (Argentine Andes.) 

Andesinite, Turner, 1900. -- A phanerocrystalline 
rock composed almost entirely of andesine. 

Andesite, Von Buck, 1826.- A volcanic rock, gener- 
ally porphyritic, composed essentially of plagioclase 


(andesine or oligoclase, or having an average com- 
position corresponding to those types), together 
with one or more of the mafic minerals, biotite, 
hornblende, and pyroxenes. The modern primary 
distinction between andesite and basalt does not 
depend on the absence or presence of olivine, or 
on the relative proportions of felsic to mafic 
minerals (though each of these criteria have been 
applied in the past), but on the composition of 
the plagioclase. (Andes.) 

J. J. H. Teall : Geol. Mag., 1883. pp. 100, 145, 252, 344. 

J. P. Iddings : Journ. Geol., i, 1893, p. 166. 

J. W. Sollas : Rocks of Cafe Colville Peninsula, New Zea- 
land, 1905. 

Mem. Geol. 9 Surv. Scot. 53 (Ben Nevis and Glen Coe), rgi6, 
p. 180. 

. An achondritic meteoritic stoiie consisting 
mainly of purple titaniferous augite (over 90 per 

. cent.) and olivine. 

Anhedral, Pirsson, 1895. See Allotriomorphic. 

Anhedron, Pirsson, 1895. A term applied to crystals 
which have failed to develop the faces naturally 
suggested by the term crystal. 
L. V. Pirsson : Bull. Geol. Soc. Am., vii. 1895, 492. 
Ankaramite, Lacroix, 1916. A melanocratic basaltic 
rock, poor in plagioclase and richer in augite than 
in o\i\me=felspathic augitite. 

(Ankaramy, Madagascar.) 
A. Lacroix : C.R., clxiii, 1916, p. 182. 

Ankaratrite, Lacroix, 1916. -- Melanocratic forms of 
nepheline-basalt with phenocrysts of olivine ; some 
varieties contain melilite. 

(Mt. Ankaratra, Madagascar.) 
A. Lacroix : C.R., clxiii, 1916, p. 256. 

Anorthite-basalt, Wada, 1882. A variety of basalt, 

containing anorthite (An 90 -An 100 ) as the essential 

felspathic mineral. (Fuji Yama, Japan.) 

Anorthite Rock, Irving, 1883. -- A variety of anor- 

thosite, consisting mainly of anorthite. 

(L. Superior, Minnesota.) 
R. D. Irving : U.S.G.S., Man. v, 1883, p. 59. 


Anorthosite, Sterry Hunt, 1863. -- A leuoocratic 
gabbro or norite, nearly free from pyroxene, and 
thus composed essentially of a plagioclase (Fr. 
= anorthose), which is usually not less calcic than 

N. L. Bowen : Journ. GeoL, xxv, 1917, p. 209. 
Anthracite. A variety of coal, containing- less than 
10 per cent, of volatile matter and over 90 per 
cent, of carbon, and which therefore burns slowly 
with a smokeless flame. Anthracite can be 
handled without soiling the fingers and has a high 
A. Strahan : Mem. Geol. Surv. (Coals, S. Wales), 1915, 

P- 73- 
Anthraconite. A term applied to black bituminous 

limestones or marbles. 

Anthraxolite. - - A coal-like and lustrous variety of 
bitumen; 11=3 4; S.G.= nearly 2. The same 
term has also been used to describe bituminous 
and anthracitic matter occurring as enclosures in 
igneous rocks. 

Anti-Stress Minerals, Barker, 1918. A term sug- 
gested for minerals such! as anorthite, potash- 
felspars, pyroxenes, forsterite, andalusite, etc., 
whose formation in metamorphosed rocks is fav- 
oured by conditions controlled, not by shear- 
ing stress, but by thermal action and hydrostatic 
pressure ; contrasted with stress-minerals (q.v.). 
A. Harker : Q.J.G.S., Ixxiv, 1918, p. Ixxviii. 
Apachite, Osann, 1896. A variety of nepheline-phoncv 
lite, rich in alkali-pyroxenes and amphiboles. 

(Apache Mts., Texas.) 

Aphanite, Haiiy, 1822. A term first applied to com- 
pact rocks of dioritic composition ; now extended 
to any fine-grained igneous rock or groundmass 
(said to be aphanitic), the constituents of which 
cannot be distinguished by the unaided eye. 
Aphrolith, Jaggar, 1917. A term, meaning "foam- 
stone, ' ' applied to block-lava or aa-lava. 
T. A. Jaggar : Jour. Wash. Acad. Sci., vii, 1917. 


Aplite, Retz. -- A leucocratic microgranite occurring 
as dykes or contemporaneous veins ; muscovite 
may be present. Sometimes written Haplite. 

Aplodiorite, Bailey, 1916. A leucocratic variety of 
biotite-granodiorite containing little or no horn- 

E. B. Bailey : Mem. Geol. Surv. Scotland, 53 (Ben Nevis & 
Glen Coe), 1916, pp. 160, 166. 

Aplogranite, Bailey^ 1916. -- A term for leucocratic 
rocks of granitic texture consisting essentially of 
alkali-felspar and quartz, with subordinate biotite ; 
muscovite may be present or absent. 
E. B. Bailey : Mem. Geol. Surv. Scotland, 53 (Ben Nevis & 
Glen Coe), 1916, p. 158. 

ApO-. A prefix implying the derivation of one kind of 
rock from another ; applied specifically to the 
names, of volcanic rocks to indicate that they have 
suffered devitrification, e.g., aporhyolite. Van 
Hise proposed aposandstone for quartzite, apogrit 
for grauwacke, and other analogous terms. 
F. Bascom : Journ. Geol., i, 1893, p. 828. 
C. R. Van Hise : U.S.G.S. Mon. 47, 1904, p. 776. 

Apophyses. - - Veins, tongues, or dykes that can be 
directly traced to larger intrusions, from which 
they are offshoots. 

Appinite, Bailey, 1916. -- A group term for melano- 
cratic varieties of syenite, monzonite or diorite, 
which are rich in hornblende ; like the vogesites 
and spessartites, of which appinite is regarded as 
the " plutonic " equivalent, secondary minerals 
are generally present. (Appin, Loch Linnhe.) 

Mem. Geol. Surv. Scot., 53 (Ben Nevis and Glen Coe), 1916, 
pp. 167-8. 

Aqueo-igncOUS. A term applied to minerals which are 
of magmatic origin, and yet are not strictly pyro- 
genetic because of their deposition from solutions, 
which, though late-magmatic, are rich in water. 
Amygdales and pegmatites afford examples. 
Applied also to rocks formed of such minerals and 
to the processes operative in their formation. 


Arapahite, Washington &> Larsen, 1913. A 
melanocratic variety of basalt, containing about 
50 per cent, of magnetite. 

H. S. Washington & E. S. Larsen : Journ. Wash, Acad. 
Sci., iii, 1913, p. 449. 

Arctic Suite, ^. Wolff, 1914. A general term for the 
basaltic and associated rocks of the Brito-Arctic 
province, drawing attention to the fact that they 
do not clearly belong to either the Atlantic or the 
Pacific suite, but occupy a petrographic position of 
an intermediate character corresponding with their 
geographical situation between the alkali-rocks of 
the Atlantic Islands and the andesitic-rocks of the 
Pacific Borders. 

F. v. Wolff : Der Vulkanismus, Bd. I (2), 1914, p. 427. 

A. Holmes : Min. Mag., xviii, 1918, p. 180. 

Arenaceous = Psammitic. -- Terms applied to sedi- 
mentary rocks composed of grains of sand, loose 
or cemented. 

Argillaceous = PelitlC. Terms applied to sedimentary 
rocks characterised by an abundance of clay 
minerals, and a predominance of the " mud " 

W. M. Hutchings : Geol. Mag., 1890, pp. 264, 316: 1891, p. 
164; 1892, pp. 154, 218; 1894, pp. 36, 64; 1896, pp. 
39, 343- 

Argillite. An argillaceous rock cemented by silica, 
and therefore more compact and less clearly 
laminated than shale. 

Ariegite, Lacroix, 1901. A type of pyroxenite rich in 
alumina, containing variable amounts of spinel, 
pyrope, and sometimes of hornblende. 

(Ariege, Pyrenees.) 

A. Lacroix : Cong. Geol. Inter., C.R. viii (Paris, 1900), 1901, 
p. 807. 

Arizonite, Spurr & Washington, 1917. A dyke 
rock, containing 80 per cent, of quartz and 18 per 
cent, of orthoclase. (Arizona.) 


Arkite, Washington, 1901. - - A holocrystalline por- 
phyritic rock), composed of leucite (or pseudo- 
leucite), nepheline, cegirine-augite and melanite. 

(Magnet Cove, Arkansas.) 
H. S. Washington : Jonrn. GeoL, ix, 1901, p. 615. 

Arkose, Brongniart, 1823. A coarse-grained richly- 
felspathic sandstone or grit, derived from the rapid 
disintegration of granite or gneiss. Arkose thus 
differs from felspathic grit and sandstone by con- 
taining a high percentage of felspar which has 
suffered little, if any, alteration by weathering. 
D. C. Barton : Journ. Geol., xxiv, 1916, p. 417. 

Arso Trachyte. A type of olivine-trachyandesite con- 
taining phenocrysts of sanidine, oligoclase, augite 
and olivine in a trachytic groundmass containing 
interstitial glass. The type is thus related to 
rhomb-porphyry and kenyte. 

(Lava of 1302, Ischia.) 

Articulite, Wether ell, 1867. = Flexible Sandstone. 

Aschaffite, G umbel, 1865. A lamprophyric dyke-rock 
containing quartz and plagioclase, with abundant 
biotite among the femic minerals. 

(Aschaffenburg, Bavaria.) 

Aschistic, Brogger, 1894. A term applied to those 
rocks of minor intrusions which have not suffered 
differentiation into leucocratic and melanocratic 
modifications, but which have nearly the same 
composition as the larger intrusions with which 
they are associated. 

Ash, Volcanic. Fine-grained pyroclastic material 
composed of comminuted glass, crystals, and/or 
cryptocrystalline or micro-crystalline rock sub- 
stance. The term is, however, becoming obsolete, 
partly because of its ordinary connotation, and 
partly because in British literature it has not been 
confined to fine-grained material, but has been 
used synonymously with Tuff. 


Asphalt. A black, glossy, and brittle variety of 

G. H. Eldridge : U.S.G.S. 22nd Ann. Re-p., Ft. i, 1901, p. 

H. Kohler : Die Chemie und Technologie der Natiirlichen 

und Kiinstlichen Asphalte, 1913. 
H. Abraham : As-phalts and Allied Substances, 1918. 

Asphaltite. -- A group-term sometimes used for the 
solid forms of the purer bitumens, such as albe,r- 
tite, grahamite, and uintaite, to distinguish them 
from bituminous sands and limestones, which com- 
mercially are often described as " asphalt." 

Assimilation, Michel-Levy, 1893. - The process 
whereby material from the containing walls of an 
intrusion is absorbed by solution in the invading 
magma, either in situ (or nearly so) at the con- 
tacts, or in depth, ,by the sinking through the 
magma of blocks or fragments stoped from the 

W. J. Miller : Bull. Geol. Soc. Am., xxv, 1914, p. 243. 

R. A. Daly : Igneous Rocks and their Origin, 1914. 

Journ. Geol., xxvi, 1918, p. 126. 

Assyntite, Shand, 1909. A variety of augite-bearing 
sodalite-syenite. (Assynt, N.W. Highlands.) 

S. J. Shand : Trans. Edin. Geol. Soc., ix, 1910, p. 403. 

Asthenosphere, Barrell, 1914. -- A thick zone lying 
beneath the more rigid lithospherej in which 
plasticity reaches a maximum, in which isostatic 
and other readjustments are effected, and in which 
magmas may be generated. 

J. Barrell : Journ. Geol., xxii, 1914, p. 680; and xxiii, 1915, 
p. 425. 

A. Holmes : Geol. Mag., 1916, p. 267. 

J. Barrell : Am. Journ. Sci., xlviii, 1919, pp. 281, 291. 

Astite, Salomon, 1898. - - A variety of hornfels, in 
which mica and andalusite are the dominant 
minerals. (Cima d'Asta, Italian Alps.) 

Atatschite, Morozeinicz, 1901. -- A variety of hyalo- 
orthophyre, characterised by the presence of small 
amounts of sillimanite, and locally of cordierite. 


Orthoclase, augite and biotite occur as micro- 
scopic crystals in a glassy base. 

(Atatsch Mt., Southern Urals.) 

J. Morozewicz : Mem. Comm. Geol. Russia, xviii (i), 1901, 
p. 18. 

Ataxic, Keyes, 1901. A general term applied to un- 
stratified ore-deposits, as opposed to those that are 
stratified, or eutaxic. 

C. R. Keyes : Trans. Amer. Inst. Min. Eng.< xxx, 1901, 
P- 3 2 3- 

Ataxite, Loewinson-Lessing, 1888. -- A brecciated or 
irregularly mottled composite! volcanic rock, in 
which the broken fragments of one lava-flow are 
irregularly distributed in another. A similar 
structure to which the term may also be applied 
occurs in certain minor intrusions. 

Ataxite, Brezina, 1896. A general term for siderites 
(iron-meteorites) which contain less nickel than 
hexahedrites or more than octahedrites, and so fail 
to exhibit the structures characteristic of those 

Atlantic Suite, Harker, 1896. A general term for the 
whole assemblage of alkali-rocks, directing atten- 
tion to their distribution in and around the 
Atlantic, to their association with the Atlantic type 
of coast-line, and more generally to their associa- 
tion with tectonic structures due to tension, frac- 
ture and differential radial movements. Cf. 
Pacific Suite. See Alkali-rocks. 

G. T. Prior : Min. Mag., xiii, 1903, p. 228. 

A. Harker : Nat. Hist. 1 g. Rocks, 1909, p. 90. 

J. S. Flett : Geol. Mag., 1912, p. 517. 

J. W. Gregory: Scientia, xi, 1912, p. 56. 

A. Holmes: Geol. Mag., 1916, p. 272; Geol. Map., xviii, 
1918, p. 220. 

Aubrite, Prior, 1919. -- A group name for enstatite 
achondrites, including Aubres, Bishopville and 
Bustee. Cf. Chladnite. 


Auganite, Winchett, 1912. - - A term suggested for 
augite-andesite to avoid the use of a compound 

A. N. Winchell : Jonrn. GeoL, xxi, 1913, p. 215. 

Augen-gneiss. A general term for gneissose rocks, 
independently of their origin, containing " eyes," 
i.e., phacoidal or lenticular crystals, or aggre- 
gates, which simulate the porphyritic crystals of 
igneous rocks. The "eyes" may be porphyro- 
blastic or blasto-porphyritic crystals, or, in the case 
of composite gneisses, porphyritic crystals belong- 
ing to the injected component of the rock. 

Augen-SChist, Lapworth, 1885. -- A rock associated 
with mylonite, and composed of granulated 
minerals, aggregates of which occur as " augen," 
surrounded by and alternating with schistose 
streaks and lenticles of completely recrystallised 
minerals. In mylonite the rolling out has been 
effected with but little recrystallisation. Cf. 
C. Lapworth : Nature, 1885, p. 559. 

Augitite, Doelter, 1882. A volcanic rock, containing 
phenocrysts of augite and iron-ore, with or with- 
out biotite or hornblende, in a base of brown glass, 
which is usually a soda-rich variety. = Magma 
basalt (in part). 

Aureole. -- A term applied to the zone of contact- 
metamorphosed rocks surrounding an intrusion. 

Australite. A term used to distinguish the obsidian- 

ites of Australia from those of Bohemia (Molda- 

vites) and Billiton (Billitonites). Cf. Obsidianite. 

H. S. Summers : Aust. Ass. Ad. Set. (Melbourne, 1913), xiv, 

1914, p. 189. 
C. G. Thorpe : Nat. Hist, and Sci. Soc. W . Australia, 1914, 

p. 20. 
E. W. Skeats : Proc. Roy. Soc. Victoria, xxvii, 1915, p. 362. 

Authigenous, or Authigenic, Kalkovsky, 1880. 

Terms, meaning generated on the spot, applied to 
those constituents that came into existence with 
or after the formation of the rock of which they 


constitute a part; e.g. , the primary and secondary 
minerals of igneous rocks, and the cements of 
sedimentary rocks. Cf. Attothigenous. 

Autochthonous, Giimbel, 1888. -- A term applied to 
rocks such as rock-salt and stalactite, denoting 
that they and their constituents have been formed 
in situ. Cf. Allochthonous. 

Autodastic, Van Plise, 1894. A term applied to rocks 
that have been brecciated in place by mechanical 
processes, e.g. , crush breccias. 

Autolith, Holland. A fragment of igneous rock en- 
closed in another igneous rock of later consolida- 
tion, each being- regarded as a derivative from a 
common parent magma. = Cognate Inclusion. 
T. H. Holland : Mem. Geol. Siirv. India, xxviii, iqoo. p. 217. 

Autometamorphjsm, Sargent, 1917. The metamor- 
phism of an igneous rock by the action of its own 
volatile fluxes; e.g. , the' formation of spilite from 
basalt. Cf. Autopneumatolysis. 
H. C. Sargent : Q.J.G.S., Ixxiii, 1917-18, p. 19. 

Automorphic, Rohrbach, 1886. - - See Idiomorphic. 

Autopneumatolysis, Lacroix, 1907. The production 
of new minerals in an igneous rock by the action 
of its own mineralising agents; e.g., the forma- 
tion of sanidine, sodalite, biotite, etc., in the 
leucite-tephrites of Vesuvius. 

A. Lacroix : Nouv. Arch, du Mus. d^Hist. Nat., ix, 1907, 
p. 109. 

Avezacite, Lacroix, 1901. A phanerocry stall ine dyke 
rock, composed of augite and hornblende, with 
titaniferous iron-ore, apatite, and sphene as 
abundant accessories. The type-rock is cata- 
clastic in structure. (Avezac, Pvrenees.) 

A. Lacroix : Cong. Geol. Inter., C.R., viii (1900), 1901, p. 

Aviolite, Salomon, 1898. A variety of hornfels, con- 
sisting essentially of mica and cordierite. 

(Monte Aviolo, Italian Alps.) 


AxiolitlC, Zirkel, 1876. -- A term applied to a com- 
posite spherulitic texture, in which the spherulitic 
bodies are elongated along- a central axis, to 
which the radiaiting fibres are normal. 


Bahiaite, Washington, 1914. A variety of hypersthe- 
nite, containing- abundant hornblende with smaller 
amounts of olivine and pleonaste. 

(Bahia, Brazil.) 

H. S. Washington : Am. Journ. Sci., xxxviii, 1914, p. 86. 

Ballstone. A Shropshire term for an irregular len- 
ticular mass of unstratified limestone occurring- in 
the Wenlock and other Palaeozoic limestones. 
Examples vary in dimensions up to 60 feet or 
more, and are found to consist of colonies of corals 
and stromatoporoids (in the position of growth) 
enveloped in a matrix of calcareous mud. 
M. C. Crossfield & M. S. Johnston : Proc. Geol. Assoc.< xxv, 
1914, p. 193. 

Banakite, Iddings, 1895. A variety of trachydolerite 
similar mineralogically to absarokite but contain- 
ing less olivine and augite, and in some varieties 
being free from olivine, or even containing quartz. 

(Yellowstone Park.) 
J. P. Iddings : Joiirri. Geol., iii, 1895, p. 947. 

Banatite, v. Cotta. An orthoclase-bearing variety of 
augite-quartz-diorite. (Banat.) 

Bandaite, Iddings, 1913. A general term for " lab- 
radorite-dacites " ; i.e., for quartz-basalts which in 
texture resemble dacites or andesites. 

(Bandai San, Japan.) 

Banded Structure- A structure developed in many 
igneous and metamorphic rocks, due to the alter- 
nation of layers which differ conspicuously in 
mineral composition or texture, or both. 
F. F. Grout : Journ. Geol., xxvi, 1918, p. 439. 


Banket. A term of Dutch origin originally applied to 
the auriferous Witwatersrand conglomerates, and 
now used more widely for other compact siliceous 
vein-quartz conglomerates, which have pebbles of 
about the size of a pigeon's egg, and in general 
possess the megascopic characters of the type-rock 
from the Rand. 

R. B. Young :JThe Banket , London, 1917. 

W. H. Goodchild : Mining Mag., xix, 1918, p. 194. 

Barolite, Wadsworth, 1891. -- A term suggested for 
rocks composed of barytes or celestine. 

Basalt. A microlithic or porphyritic igneous rock of 
a lava flow or minor intrusion, often vesicular or 
amygd'aloidal, having an aphanitic texture as a 
whole or in the groundmass, and composed essen- 
tially of plagioclase (at least as calcic as labra- 
dorite), and pyroxene, with or without interstitial 
glass. When olivine is present the rock is termed 
an olivine-basalt. In the field the term basalt is 
generally applied only to lava flows, the corre- 
sponding rocks of minor intrusions being called 
dolerite. The original distinction between basalt 
and dolerite was based simply on degree of granu- 
larity, basalt being a compact rock, while dolerite 
was recognisably crystalline, i.e., the component 
minerals were sufficiently large to reflect light in- 
dividually, even though they were too small for 

A. Harker : Mem. Geol. Surv. Scot. (Tert. Ig. Rocks Skye), 
1904, p. 29. 

H. S. Washington : Q.J.G.S., Ixiii, 1907, p. 69 (Mediter- 

Mem. Geol. Surv. Scot. (Glasgow District), 1911, p. 135. 

G. W. Tyrrell : Trans. Geol. Soc. Glas., xiv, 1912, p. 210 
(Midland Valley). 

W. Cross : U.S.G.S., Prof. Pap., 88, 1915 (Hawaii). 

A. Holmes : Q.J.G.S., Ixxii, 1916, p. 260 (E. Africa). 

O. Backstrom : Bull. Geol. Inst. Univ. U-psala, xiii, 1916, 
p. 115 (Antarctica). 

A. Holnies : Min. Mag., xviii, 1918, p. 180 (Arctic). 


Basal tite. An old term revived by the International 
Congress in 1900, and adopted to denote basalts 
without olivine. 

Basanite, Brongniart, 1813. A basaltic rock, gener- 
ally porphyritic, containing plagioelase, augite, 
olivine, and a felspathoid ; nepheline-, leucite-, and 
analcite-basanites are distinguished. In the 
original usage of the term, olivine was not neces- 
sarily an essential component. The type is now, 
however, distinguished from tephrite by the pre- 
sence of olivme. 

Basanitoid, Bucking, 1881. A term used for alkali- 
basalts free from nepheline, but containing a soda- 
rich iso tropic base. By Lacroix it has been more 
recently denned as a basaltic rock having the 
chemical composition of basanite, but free from 

A. Lacroix : C.R., clxix, 1919, p. 402. 

Basic. A term applied to igneous rocks having a re- 
latively low percentage of silica, the limit below 
which they are regarded as basic being about 52 
per cent. Cf. subsilicic and under saturated. 

Basis. See Mesostasis. 

Batholith, Suess, 1888. A large transgressive intru- 
sion with sides generally steeply inclined, and with 
no visible or de terminable floor. Smaller intru- 
sions of similar relations are variously called 
Stocks, Bosses, or Domes. 
R. A. Daly : Igneous Rocks and their Origin, 1914, p. 89. 

Batukite, Iddings & Morley, 1917. A porphyritic vol- 
canic rock containing phenocrysts of augite and 
fewer of olivine, in a groundmass of augite, mag- 
netite, and leucite. The rock is thus a melano- 
cratic leucite-basalt. (Batuku, Celebes.) 

J. P. Iddingp & E. W. Morley : Proc. Nat. Acad. Sci. f iii, 
'Q 1 ?! P- 595- 

Bauxite, Dufrenoy, ^847. - - An amorphous mineral 
having the composition represented by 
A1 2 O 3 .2H 2 O. The name is also applied com- 



mercially to aluminous lateritic rocks in which 
aluminium hydroxides, amorphous or crystalline, 
predominate over other lateritic constituents. 
Further confusion has been introduced by pro- 
posals (a) to use bauxitite (DHtler and Doelter, 
1912) for a rock mainly composed of bauxite, and 
(b) to use bauxitite (Campbell,.!*:)!?) for the mineral 
bauxite as denned above. The latter usage is 
clearly inadmissible, and the former serves little 
purpose, as most of the rocks referred to as 
bauxite contain very little of the mineral properly 
so called, though many of them correspond to it 
in their bulk chemical composition on account of 
the presence of both A1 2 O 3 .H 2 O and A1 2 O 3 .3H 2 O. 

W. J. Mead : Econ. GeoL, x, 1915, p. 28. 

T. L. Watson : Geol. Sttrv. Georgia, Bull, n, 1916. 

J. Morrow Campbell : Mining Mag., 1917, p. 171. 

Bean Ore. A loose pisolitic iron ore of Tertiary age ; 
distinguished from mine'tte by the larger size of the 
pisolitic grains. 

Becke Method. A microscopic method of determin- 
ing which of two materials in contact has the 
higher or lower average refractive index. The 
amount of illumination is reduced and the focus 
adjusted until the contact between a mineral with 
liquid, Canada balsam, or another mineral appears 
as a relatively bright line. On raising the objec- 
tive a band of illumination moves into the material 
having the higher refractive index ; while on lower- 
ing the objective the band moves into the substance 
with the lower index. 

Beerbachite, Chelius, 1894. A fine-grained gabbro, 
often leucocratic, occurring in aplite-like veins or 
dykes ; composed essentially of labradorite and 
diallage, with hypersthene and magnetite. 

Bekinkinite, Rosenbusch, 1907. A melanocratic rock 
containing titanaugite with nepheline and a little 
felspar as essential minerals. Soda-amphibole, 
biotite and analcite are often present and most ex- 

Samuel S. Clark 


amples are olivine-bearing. By Lacroix bekin- 
kinile is regarded as a variety of theralite in which 
the dominant white mineral is analcite. 

(Bekinkina, Madagascar.) 

G. W. Tyrrell : Geol. Mag., 1915, pp. 304 and 361. 
A. Lacroix : C.R., clxx, 1920, p. 20. 

Belonite, Vogelsang, 1872. A needle-shaped crystal- 
lite with pointed or rounded ends. 

Belugite, Spurr, 1900. A term applied to rocks inter- 
mediate (in respect of their felspar) between dior- 
ite and gabbro; i.e., containing andesine and/or 
labradorite. (Beluga River, Alaska.) 

J. E. JSpurr : Amer. Geol.) xxv, 1900, p. 233. 

Bentonite. A white clay-like rock largely composed 
of colloidal silica and characterised by its capacity 
for absorbing large quantities of water. 

(Rosedale Mine, Alberta.) 

Beresite, Rose, 1840. A quartz-rich variety of aplite, 
often characterised by the presence of pyrite. 

(Beresovsk, Urals.) 

J. E. Spurr : Am. Journ. Sci., x, 1900, p. 358; U.S.G.S. zoth 
Ann. Re-p., Ft. vii, 1900, p. 195. 

Bergalite, Soellner, 1913. - - A black pitch-like dyke 
rock containing small phenocrysts of haiiyne, 
apatite, perovskite, melilite, and magnetite, in a 
groundmass of the same minerals with nepheline 
and biotite and brown interstitial glass 

(Kaiserstuhl, Baden.) 

Beringite, Hafsinskij 1912. A melanocratic variety 
of soda-trachyte rich in barkevikite. 

(Bering Is., Kamchatka.) 

Bermudite, Pirsson, 1914. A lamprophyric volcanic 
rock containing abundant small biotite crystals, 
with accessory iron-ores and apatite, in an obscure 
analcitic base. The type is thus the effusive 
equivalent of biotite-monchiquite or ouachitite. In 
some varieties augite (brown to colourless) is also 
present. (Bermuda Is.) 

V V. PirssoL. : Am. Journ. Sci.> xxxviii, 1914. p. 340. 


Berondrite, Lacroix, 1920. A type of theralite char- 
acterised by the presence of elongated crystals of 
brown hornblende associated with titaniferous 
augite. Cf. Luscladite. 

(R. Berondra, Madagascar.) 
A. Lacroix : C.R., clxx, 1920, p. 22. 

Beschtauite, Gerassimow, 1910. A soda-rich variety 
of quartz-porphyry ; = quartz-keratophyre. 

(Mt. Beschtau, Caucasia.) 

Billitonite, F. Suess, 1900. A general term for the 
obsidianites of the Malay Peninsula and Archi- 
pelago. (Billiton.) 

Binary Granite, Keyes y 1895. A term applied origin- 
ally to granites containing only the essential 
minerals quartz and felspar, but now used to con- 
note granites which contain both the common 
micas, muscovite and biotite. 

BirdVEye Slate. - - A quarry man's term for slate 
crowded with squeezed concretions. The term 
Bird's-eye is given in Guernsey to a variety of 

Birkremite, Kolderup, 1903. -- A leucocratic quartz- 
syenite containing alkali-felspars, together with 
small amounts of quartz and hypersthene. 

F. Loewinson-Lessing : Verh. Russ. Min. Ges. St. Pet., xlii, 
1905, p. 262. 

Bitumen. A group name for natural substances com- 
posed of hydrocarbons, ranging in types from 
petroleum (mobile), through mineral tars (viscous), 
to asphalt (rigid). 

G. H. Eldridge : U.S.G.S. 22nd Ann. Re-p., Pt. i, 1901, p. 


H. Kohler : Die Chemie und Technolgie der Naliir lichen 
und Kiinstlichen As-phalte, 1913. 

Black-band Ironstone. A variety of clay ironstone 
containing sufficient carbonaceous matter to allow 
of calcining without the addition of fuel in a separ- 
ate charge. 


Blaes. A Scottish name for carbonaceous shales of a 
grey-blue colour, associated in the Lothians with 
oil-shales. They differ from the latter in having 1 a 
low content of bituminous matter, in being- brittle 
rather than tough, and in weathering- to a crumb- 
ling- mass which passes into soft clay. 
Mem. Geol. Surv. Scotland (Oil Shales, Lothians), iQi2> 
p. 7. 

Blairmorite, MacKenzie, 1919. A porphyritic volcanic 
rock characterised by an abundance of analcite 
phenocrysts, in a groundmass of analcite, alkali- 
felspar and alkali-pyroxenes. 

(Blairmore, Crowsnest Pass, Alberta.) 
Geol. Surv. Canada, Museum Butt. No. 4, 1914, p. 19. 

Blast. A syllable indicating the process of recrystal- 
lisation in a highly viscous mass during- the meta- 
morphism of rocks. It is used as a suffix in terms 
like idioblast and porphyroblast to indicate the 
form or relations of individual crystals. The 
termination -blastic is used in words like grano- 
blastic and poikiloblastic to denote the textures of 
the rocks produced. As a prefix, blasto-, it appears 
in terms like blastophitic and blastoporphyritic to 
connote a relict texture veiled, but not entirely 
destroyed by recrystallisation. 
U. Grubenmann : Die Kristattinen Schiefer, i, 1904. 

Blasto-porphyritic, Becke, 1903. A term applied to 
the textures of metamorphic rocks derived from 
porphyritic rocks, and in which the porphyritic 
character still remains as a relict feature, veiled 
but not obliterated by subsequent recrystallisation. 

Block-lava. A term applied to lava flows which occur 
as a tumultuous assemblag-e of angular blocks 
having extremely rough surfaces due to the abun- 
dant development of large vesicles; = aa-lava or 
aphrolithic lava. 

Blue Ground. A term applied to the slaty-blue or blue- 
green kimberlite-breccia of diamond pipes, occur- 


ring" beneath a superficial oxidised covering known 
as Yellow Ground. (Kimberley.) 

P. A. Wagner : The Diamond Fields of South Africa, 1914 
p. 26. 

Blue Mud.- A common variety of deep-sea mud hav- 
ing- a bluish-grey colour due to the presence of or- 
ganic matter and finelv-divided iron-sulphides ; 
CaCO 3 present in variable amounts up to 35 
per cent. 

J. Murray & A. F. Renard : " Challenger " Rep. (Deep Sea 
Deposits), 1891, p. 229. 

Bogen Structure, Milgge. A term for the structure 
of vitric tuffs composed largely of shards and 
" bows " of glass, formed by the explosive vesicu- 
lation of lavas, or by the breaking of pumice or 
other highly vesicular vitreous rocks. 

Bog Iron Ore. A g-eneral term for impure ferruginous 
deposits formed in bogs or swamps by the oxidis- 
ing action of al"ae, bacteria, or the atmosphere. 
In the presence of decavingf vegetation, which acts 
as a reducine aeent, siderite is deposited. 
E. C. Harder : U.S.G.S., Prof. Pap. 113, 1919. 

Bojite, Weinschenk. - - A term suggested for horn- 
blende-gabbros in general. The type rock con- 
tains augite and biotite in addition to hornblende. 

Bole. A bright-red, waxy or unctuous decomposition 
product of basaltic rocks, having the variable com- 
position of lateritic clays. 
Mem. Geol. Surv. Ireland (Interbasaltic Rocks), 1912, p. 18.' 

Bombs. Ellipsoidal, discoidal, or irregularly rounded 
masses of lava ejected at a high temperature dur- 
ing a volcanic eruption. Bombs vary in size from 
that of the largest lapilli upwards. They are char- 
acterised by a well-defined crust, and are often 
cellular or even hollow, internally. 

Boninite, Peter sen, 1891. A hyalo-andesite with occa- 
sional phenocrysts of andesine and hypersthene. 

(Bonin Is., Japan.) 


Borolanite, Teall, 1892. A phanerocrystalline igneous 
rock composed essentially of orthoclase and mela- 
nite with subordinate nepheline, biotite, and pyrox- 
ene. Orthoclase and nepheline (or sodalite) 
sometimes form rounded pseudo-porphyritic masses 
resembling- leucite. (L. Borolan, Assynt.) 

S. J. Shand : Trans. Edin. Geol, Soc., ix, 1909, p. 202, and 
1910, p. 376. 

BOSS. A transgressive intrusion of igneous rockjike 
a stock or dome. The term is also applied to 
forms of less regular outline than the latter, and is 
therefore of wider application. 

Bostonite, Rosenbusch, 1882. A leucocratic alkali- 
syenite-aplite with trachytic texture ; formed almost 
wholly of alkali-felspars. (Boston, Mass.) 

Boulder Clay. - - A tenacious unstratified deposit of 
glacial origin consisting of a stiff clay (rock flour) 
packed with subangular stones of varied sizes. 

Bowenite. A translucent variety of serpentine com- 
posed of a dense felt-like aggregate of colourless 
serpentine-fibres, with occasional patches of mag- 
nesite, flakes of talc, and grains of chromite. The 
rock occurs as veins in a foliated rock containing 
the same minerals, but with talc as the dominant 
constituent. (New Zealand.) 

A. M. Finlayson : Q.J.G.S., Ixv, 1909, p. 361. 

Bowralite, Ma-wson, 1906. A pegmatoid rock consist- 
ing of idiomorphic sanidine with subordinate soda- 
amphibole (arfvedsonite) and agirine. 

(Bowral, N.S. Wales.) 
D. Mawson : Proc. Linn. Soc. N.S.W., xxxi, 1906, p. 606. 

Box-Stones. -- A local (Suffolk) name for masses of 
brown ferruginous or phosphatic sandstone, 
rounded or flattened in form, and in size generally 
a little larger than that of the closed fist. Some 
specimens are more concretionary than others, 
and, on being broken, are found to enclose fossil 
remains : hence the name. 
P. G. H. Boswell : Geol. Mag., 1915, p. 250. 


Braccianite, Lacroix, 1917. - - A variety of leucite- 
tephrite, having- the chemical composition of cer- 
tain leucitites. (Bracciano, Italy.) 
A. Lacroix : C.R., clxv, 1917, p. 1030. 

Breccia. A clastic rock made of coarse angular or sub- 
angular fragments of varied or uniform composi- 
tion, and of either exogenetic (e.g., scree or mo- 
raine breccias) or endogenetic origin (e.g., volcanic 
or crush-breccias). 

T. G. Bonney : Q.J.G.S., Iviii, 1902, p. 185. 

W. H. Norton : Journ. Geol., xxv, 1917, p. 160. 

Bronzitite, Lacroix, 1894. A rock composed wholly 
or almost wholly of bronzite. 

A. Lacroix : Nouv. Arch. Mus. d'Hist. Nat., vi, 1894, p. 304. 

Brotocrystal, Lane, 1902. A term applied to crystals 

having corroded or embaved outlines. 
A. C. Lane : Bull. Geol. Soc. Am., xiv, 1902, p. 386. 

Brown Cpal, see Lignite. Brown coal is now distin- 
guished chemically from bituminous coal by con- 
taining more than 10 per cent, of water ; and from 
lignite by containing less than 20 per cent. 

Buchite. A vitrified rock produced from phyllite or 
other material by intense local heat due to contact 
with basalt magma, or to the thermal effects* of 
friction in mylonised crush-belts. 
J. S. Flett : Mem. Geol. Surv. Scot. (Oban), 1908, p. 129. 

Buchnerite, Wadsworth, 1884. A term for peridotites 
containing both monoclinic and ortho-rhombic 
pyroxenes. The term has not been adopted, as 
Lherzolite has priority. 

Buchonite, Sandberger, 1872. A variety of tephrite 
^ containing hornblende and biotite in addition to 
the usual minerals, plagioclase, nepheline, and 
augite. *" 

Buhr-Stone. A name given to certain varieties of 
porous open-textured calcareous sandstones which, 
on account of the angular character of the grains, 
are suitable for millstones. 


BllStite, Tschermak, 1883. An achondritic meteorite 
composed essentially of enstatite, with small 
amounts of diopside and oligoclase, and a little 
nickel-iron. Cf. Aubrite. 

Bysmalith, Iddings, 1898. An injected intrusion 
bounded by faults, and having- a roughly cylindri- 
cal or plug-like form. 
J. P. Tddings : Journ. Geol., vi, 1898, p. 704. 

Calc-alkali Rocks. A term applied to igneous rocks 
in which the proportions of lime and alkalies (in 
relation to the other constituents) are such that the 
dominant minerals are felspars, hornblende, and/ 
or augite, specifically alkali-minerals such as fel- 
spathoids and soda-pyroxenes and amphiboles be- 
ing absent. The term comprises such rocks as 
granodiorite, syenite, diorite, and gabbrp, and their 
volcanic analogues, and excludes alkali and spilitic 
rocks, and most peridotites. The term is used 
rather loosely to contrast rocks that are not " al- 
kaline " with those that are, and cannot be strictly 
limited by definition. 

Calc-aphanite. A doleritic or diabasic rock which has 
been largely replacecTby carbonate-minerals. 

Calc-flinta, Barrow. A very fine-grained metamorphic 
rock of flinty aspect derived from a calcareous 
mudstone. The new minerals are in part due to 
pneumatolytic processes, and include felspars and 
calc-silicate-minerals, the latter being less abundant 
than in calc-silicate-hornfels. 

G. Barrow & H. H. Thomas : Min. Mag., xv, 1908, p. 113. 
Mem. Geol. Surv., 347 (Bodmin and St. Austell), 1909, pp. 

86 and 97. 

Mem. Geol. Surv. 335-336 (Padstow and Camelford), 1910, 
P- 5i- 

Calciphyre, Brongniart, 1813. A crystalline limestone 
containing conspicuous calc-silicate minerals such 
as forsterite, pyroxene, garnet, etc. 


Calcite-trachyte, Washington, 1917. - - A variety of 
trachyte containing- over 10 per cent, of calcite, 
probably primary. (Bilbao, Spain.) 

Calcrete, Lamplugh, 1902. A term suggested for con- 
glomerates formed by the cementation of superfi- 
cial gravels by calcium carbonate. The term 
Calcicrcte is suggested by Bonney as preferable. 
G. W. Lamplugh : Geol. Mag., 1902, p. 575. 
Mem. Geol. Surv. Ireland, 112 (Dublin), 1903, p. in. 

Calc-SChist, Brongniart, 1827. A metamorphosed 
argillaceous limestone in which calcite has recry- 
stallised in elongated or platy forms, rather than 
in the commoner granular forms, thus giving to 
the rock with the other products of metamorphism 
a schistose structure. 

Calc-silicate-hornfels. An old term for contact-meta- 
morphic rocks of variable but generally fine grain, 
derived from marls and other calcareous sedi- 
ments, and therefore containing a great variety of 
minerals, mostly calc-silicates. 

Caliche. A deposit occurring in the Chilian nitrate- 
fields consisting of alluvium cemented with sodium 
nitrate and chloride and other soluble salts. In 
places, owing to recrystallisation, high-grade 
saline layers nearly free from debris are associated 
with the normal type of the deposit. 
J. T. Singewald & B.' L. Miller: Econ. Geol., xi, 1916, p. 

Campanite, Lacroix, 1912. A sodi-potassic variety of 
leucite-tephrite sometimes containing large pheno- 
crysts of leucite. (Mte. Somma.) 

A. Lacroix : C.K., clxv, 1917, p. 1030. 

Camptonite, Rosenbusch, 1887. A lamprophyre es- 
sentially composed of plagioclase (generally labra- 
dorite) and brown hornblende (generally barkevi- 
kite). (Campton, New Hampshire.) 

T. S. Flett : Trans. Roy. Soc. Edin., xxxix, 1900, p. 865. 
V. Hackmann : Bull. Comm. Geol. Finlande, xlii, 1914. 


Canada-Balsam. A transparent and fluid oleo-resin 
yielded by a North American species of silver fir ; 
used for mounting microscopic preparations and 
for cementing glass in optical instruments. Ex- 
posed to the air, Canada-balsam becomes brittle 
and discoloured, and its refractive index gradually 
increases. The average values for refractive index 
are 1.524 (uncooked), 1.538 (slightly undercooked), 
and 1.543 (overcooked). In slides 30 years old 
the value rarely exceeds 1.543; but for normally 
cooked balsam the refractive index is between 
1.534 and 1.540. 
A. Johannsen : Journ. Geol., xx, 1912, p. 89. 

Canadite, Quensel, 1913. A nepheline-syenite contain- 
ing albite or an albite-rich plagioclase as the 
principal felspar with abundant mafic minerals 
which contain lime and alumina (i.e., normative 
anorthite) ; the type is intermediate between albite- 
nepheline-syenite and shonkinite. 

(Almunge, Sweden, and Ontario, Canada.) 
P. Quensel : Bull. Geol. Inst. U-psala, xii, 1913, p. 163. 
Cancrinite-Syenite, Tornebohm, 1883. A variety of 
felspathoid-svenite having cancrinite as the domi- 
nant felspathoid. 
I. G. Sundell : Bull. Comm. Geol. Finlande, No. 16, 1905. 

Canga. A Brazilian term for a ferruginous breccia ^or 
conglomerate composed of fragments of haematite 
and itabirite cemented together by limonite or 
haematite, and occasionally by other lateritic con- 

Cannel Coal. A dull lustreless variety of coal which 
breaks with a conchoidal fracture. It is rich in 
volatile combustibles, and burns with a bright 

'Mem. Geol. Surv., Spec. Re<. Mineral Resoiirces of Great 

Britain, vii. 1918. 
Cantalite, Dujrenoy, 1845. - - A variety of rhyme- 

pitchstone. (Cantal.) 

A. Lacroix : C.R., 163, 1916, p. 47- 


Carmeloite, Laws on, 1893. A variety of augite-an- 
desite or basalt (according as the plagioclase is 
andesine or labradorite) characterised by the pre- 
sence of iddingsite. (Carmelo Bay, California.) 
A. C. Eawsoni : Bull. Dept. Geol. Univ. California, i, p. 
38, 1893. 

CaSCadite, Pirsson, 1905. A lamprophyre ( = olivine- 
augite-minette) with abundant phenocrysts of bio- 
tite and fewer of olivine and augite in a ground- 
mass principally composed of alkali-felspar. 

(Highwood Mts., Montana.) 
L. V. Pirsson: U.S.G.S., Bull. 237, 1905, p. 109. 

Cataclastic, Kjerulf. A term applied to the structures 
produced in a rock by the action of severe mecha- 
nical stress during dynamic metamorphism, char- 
acteristic features being the deformation and 
granulation of the minerals. The term is also 
applied to rocks characterised by such structures. 

Cataclastic, Teall, 1887. A term applied to clastic 
rocks, the fragments of which have been produced 
by the fracture of pre-existing rocks by earth- 
stresses; e.g., crush breccias. 

Catapleiite-Syenite, Tornebohm, 19/36. A porphyritic 
rock of tinguaite-habit containing phenocrysts of 
catapleiite, and occasionally of eudialyte, in an 
aphanitic but holocrystalline groundrriass com- 
posed of those minerals with alkali-felspars, 
nepheline, and aegirine. 

(Korra Karr, Sweden.) 

A. E. Tornebohm : Sveriges Geol. Under*., Ser. C., No. IQO, 

Catawberite, Lieber. A metamorphic rock consisting 
mainly of talc and magnetite. (S. Carolina.) 

Catlinite. A red variety of siliceous clay occurring in 


Cauldron-subsidence. The sinking of part of the roof 
of an intrusion within a closed system of peri- 
pheral faults up which magmas have penetrated. 
C. T. Clough, H. B. Maufe & E. B. Bailey : QJ.G.S., Ixv, 

1909, p. 611. 
E. B. Bailey : Geol. Mag., 1919, p. 466. 

Cecilite, Cordier, 1868. A variety of leucitite charac- 
terised by an abundance of melilite. 

H. S. Washington : Carnegie Inst. Wash. Pub., 57, 1906, 
P. 138- 

Celyphitic, see Kelyphitic. 

Cement. A term applied, as in mortar and concrete, 
to the material binding together the allogenic frag- 
ments or particles of clastic rocks. The term is 
not used for the groundmass, matrix, or base of 
igneous rocks. The process of cementation is the 
filling of interstices in porous or shattered rocks. 

Cenotypal, Brogger, 1894. A general term applied to 
aphanitic and porphyritic igneous rocks having the 
habit or suite of characteristics typical of fresh or 
nearly-fresh volcanic rocks such as those of Recent 
and Tertiary age. Crystals are lustrous, and 
glass, where present, has not lost its brilliancy by 
devitrification ; whereas in the older rocks felspars 
and glass have become dull and lustreless by 
decomposition and devitrification. Rocks having 
the older-looking, dense and compact habit are 
described as paleotypal. The two terms constitute 
an attempt to express the essential differences 
between the two groups of aphanitic rocks vari- 
ously distinguished as Tertiary and pre-Tertiary, 
fresh and altered, hypabyssal and volcanic : differ- 
ences that are recognised in the nomenclature of 
rocks by two groups of terms such as rhyolite and 
quartz-porphyry, andesite and porphyrite, basalt 
and diabase. 

Centric, Becke, 1878. A textural term applied to the 
arrangement of crystalline matter in regular 


groups around or about a centre, as in spherulites, 
variolites, oolites, etc. 

Ceratophyre, see Keratophyre. 

Chadacrysts, Iddings, 1909. The relatively small 
crystals scattered as poikilitic inclusions through a 
host crystal (oikocryst) of another mineral. 

Chalk. A fine-grained somewhat friable foraminiferal 
limestone of Cretaceous age occurring in Britain, 
north-western Europe and elsewhere. 

Mem. Geol. Surv. (Cretaceous Rocks of Britain), Vol. 2, 1903, 
p. 499; Vol. 3, 1904, p. 302. 

Charnockite, Holland, 1893. -- A granular variety of 
hypersthene-granite, composed of hypersthene, 
microcline-perthite, quartz and iron-ores. " Named 
after Job Charnock, the founder of Calcutta, whose 
tombstone (1695) was the first specimen of the rock 

T. H. Holland : Mem. Geol. Surv. India, xxviii, Pt. 2, 
1900, p. 134. 

H. S. Washington: Am. Journ. Sci., xli, 1916, p. 323. 

F. L. Stillwell : Aust. Ant. Exped. Set. Kef. A, iii i (i) 
(Met. Rocks, Adelie Land), 1918, p. 193. 

Charnockite Series, Holland, 1900. A series of rocks 
resembling the pyroxene-granulites of Saxony, 
ranging from charnockite through norite-like types 
to pyroxenite and characterised throughout by the 
presence of hypersthene. 

Chassignite, Rose, 1863. -- An achondritic meteorite 
essentially composed of olivine (enclosing chro- 
mite) ; nickel-iron is absent, and the type thus 
resembles the terrestrial dunite. 

Chert. A more or less pure siliceous rock composed 
in part of fibrous and radial chalcedony with or 
without the remains of siliceous and other organ- 
isms such as sponge spicules or radiolaria ; occur- 
ring as independent formations and also as nodules 
and irregular concretions in formations (generally 
calcareous) other than the Chalk. The fracture is 


generally splintery rather than conchoidal. Cf. 

W. Hill : Proc. Geol. Assoc., xxii, 1911, p. 61. 
I E. F. Davis : Bull. Dept. Geol. Univ. Calijornia, xi, p. 

235, 1918. 

Chiastolite-slate. A contact metamorphic rock, gener- 
ally free from conspicuous cleavage or schistosity, 
formed from carbonaceous shales, and containing 
conspicuous crystals of chiastolite in a generally 
cryptocrystalline groundmass. 

Mem. Geol. Surv., 338 (Dartmoor), 1912, pp. 46 and 52. 

A. Brammall : Geol. Mag., 1915, p. 224. 

Chibinite, Ramsay, 1894. A coarse-grained variety 
of eudialyte-syenite in which soda-amphiboles are 
more abundant than soda-pyroxenes. It differs 
from lujaurite in having a more granular texture, 
and in containing rather less nepheline. 


W. Ramsay : Fennia, xv, 2, p. 15. 

China-clay. Although some ambiguity still exists as 
to the exact use of the term china-clay, it is now 
customary to regard it as a commercial term for 
the clay obtained from China-clay Rock after wash- 
ing. In Europe the term kaolin is sometimes used 
for the clay both before and after washing. See 

China-clay Rock. A term applied to thoroughly 
kaolinised granite, essentially composed of quartz 
and kaolin, and in Cornwall containing also gilber- 
tite and white mica, and often tourmaline ; the 
rock is soft and can easily be crumbled in the 

J. A. Howe : Mem. Geol. Surv. (Kaolin, China Clay and 

China Stone), 1914, p. 12. 

China-Stone. A term applied to any firm granitic rock 
used in the manufacture of china, and usually, 
but not necessarily, kaolinised ; the rock does not 
crumble readily like china-clay rock ; Cornish 
varieties contain white mica and fluorite. 

J. A. Howe : Mem. Geol. Surv. (Kaolin, China Clay and 
China Stone), 1914, p. 135. 


Chladnite, Rose, 1863. A group name for achondritic 
meteorites composed essentially of enstatite. 
Brezina extended the term to include bronzite 
stones of the diogenite group. To avoid confusion 
Prior proposes the term Aubrite to replace Chlad- 
nite as used by Rose and Tschermak. 

Chlorite-SChist. -- A schist composed largely of 
chlorite, the foliation being due to the parallel dis- 
position of the flakes. Other minerals are gener- 
ally present, such as quartz, epidote, magnetite 
and garnet, the two latter being often in con- 
spicuous idiomorphic crystals (porphyroblastic tex- 

Chloritisation. -- The sum of the processes whereby 
mafic minerals are altered to minerals of the 
chlorite group, or whereby any minerals are re- 
placed by chlorite. 
G. H. Williams : U.S.G.S. Bull., 62, 1890. 

ChlorQphyre, Dumont. -- A green variety of quartz- 
diorite-porphyrite occurring at Lessines, Belgium. 

Chondrite, Rose, 1864. A general term for meteoric 
stones which contain chondrules (see below) em- 
bedded in a finely crystalline matrix consisting 
essentially of pyroxenes (mainly enstatite or 
bronzite), olivine, and nickel-iron with accessory 
troilite, chromite and oligoclase. Glass (? maske- 
lynite) is sometimes present, and in the chondrules 
may even become abundant. On the basis of the 
ratio MgO/FeO in magnesium silicates and the 
ratio Fe/Ni in nickel-iron, Prior has divided 
chondrites into four groups containing respectively 
the following percentages of nickel-iron : over 20 ; 
between 20 and 10, between 10 and 6 and less 
than 6. In these groups the proportion of nickel 
steadily increases as the percentage of nickel-iron 
decreases. See Table on p. 284. 
G. T. Prior : Min. Mag., xviii, 1916, p. 26. 


Chondrules, Rose, 1864. Spheroidal aggregates, 
often radiated in texture, varying in size from 
microscopic dimensions to about that of a walnut, 
which occur in many stony meteorites. The chief 
minerals present are orthorhombic pyroxene and 
olivine, with variable amounts of nickel-iron, 
troilite, and oligoclase ; in some cases glass 
(? maskelynite) of felspathic composition is an 
abundant constituent. 

Chonolith, Daly, 1905. A general term for injected 
igneous intrusions, having shapes so irregular or 
relations to the invaded formations so complex that 
terms like dyke, laccolith, bysmalith, etc., are not 
R. A. Daly : Igneous Rocks and their Origin, 1914, p. 84. 

Chrome-chert, Fermor, 1919. A variety of chert 
which has replaced the silicate-minerals of a 
chromite-peridotite, the more resistant chromite 
grains remaining unaltered in the secondary 
siliceous matrix. (Singhbhum, India.) 

L. L. Fermor. : Proc. Asiatic Soc. Bengal, xv, 1919, p. 

Ciminite, Washington, 1896. An olivine trachydoler- 

ite containing phenocrysts of augite, olivine, and 

orthoclase-mantled labradorite in a trachytic 

groundmass. (Mt. Cimini, Italy.) 

H. S. Washington : Journ. Geol., iv. 1896, p. 834. 

Cipolino. A marble rich in silicate minerals, and 
characterised more particularly by layers rich in 
micaceous minerals. In France the term Cipolin is 
used for crystalline limestones generally. 

Clarain, Stopes, 1919. - - A term suggested for the 
finely banded variety of " bright " coal. In 
bituminous coals it occurs as bands of variable 
thickness which have a smooth, shining surface 
when broken at right angles to the bedding plane. 
The type differs from vitrain in being minutely 
banded and containing intercalations of fine 
duratn. In thin section clarain appears translucent 



and shows a great variety of disintegrated plant 
substances, bands of spores and other constituents, 
the prevailing colours seen when the section is 
sufficiently thin being tints of yellow to reddish- 
Marie C. Stopes : Proc. Roy. Soc. B., xc, 1919, pp. 474-5. 

Class, C.I.P.W., 1902. A division of igneous rocks 
based on the relative proportions of the salic and 
femic standard normative minerals as calculated 
from chemical analyses. The descriptive terms 
used, persalic, dosalic, salfemic, dofemtc, and per- 
femic, correspond to the terms perfelsic, dofelsic, 
mafelsic, domafic, and permafic, which are based 
on the relative proportions of the felsic and mafic 
minerals actually present. The division of 
igneous rocks into classes is analogous to the less 
rigid division into hololeucocratic, leucocratic, 
mesocratic, melanocratic, and hclomelanocratic 


FELSPARS F. C. Calkins : Journ. Geol., xxv, 1917, p. 157. 
IGNEOUS INTRUSIONS R. A. Daly : Journ. Geol., xiii, 1905, 

p. 485. 
IGNEOUS ROCKS W. Cross : Q.J.G.S., Ixvi, 1910, p. 470. 

A. Holmes: Geol. Mag., 1917, p. 115. 
METAMORPHIC PROCESSES R. A. Daly: Bull. Geol. Soc. Ant. 

xxviii, 1917. p. 375. 

MINERALS W. H. Emmons : Econ. Geol., in, 1908, p. 611. 
E. T. Wherry & S. T. Gordon : P*oc. A cad. 

Nat. Sci., Philadelphia, 1915, p. 426. 
ROCKS T. Crook : Min. Mag., xvii, 1914, p. 55. 
VOLCANIC EXHALATIONS F. C. Lincoln : Econ. Geol., ii, 

1907, p. 258. 
For additional references see under individual subjects. 

Clastic. A term applied to rocks composed of frag- 
mental material derived from pre-existing rocks, 
or from the dispersed consolidation products of 
magmas (e.g., in explosion-tuffs and flow- 
breccias). Cf. autoclastic, epiclastic, caiaclastic, 


Clay. - - An earthv deposit of extremely fine texture 
which is usually plastic when wet, and becomes 
hard and stone-like on being- heated to redness. 
Chemically it is characterised by containing- hy- 
drous silicates of alumina in considerable quantity, 
with felspars and other silicates and quartz, and 
variable amounts of carbonates and ferruginous 
and organic matter. A proportion of the consti- 
tuents is generally in the colloidal state, and then 
acts as a lubricant to the grains and flakes of non- 
colloidal material. 

E. R. Buckley : Wisconsin Geol. and Nat, Hist. Surv. Bull., 
vii, Pt. i, 1901. 

H. Ries : Clays, Occurrence, Properties and Uses, 2nd Ed., 
New York, "1908. 

J. W. Mellor : Trans. Ceramic Soc., viii, 1908. 

H. E. Ashley: U.S.G.S., Bull. .388, 1909. 

A. B. Searle : British Clays, Shales and Sands, London, 

W. Salomon : Geol. Rund., vi, 1916, p. 398. 

N. B. Davis : Trans. Amer. Inst. Min. Eng., li, 1916, p. 

W. S. Boulton : Trans. Ceramic Soc., xvi, 1916-17, p. 237. 

A. H. Cox : Geol. Mag., 1918, p. 56. 

H. S. Washington : Journ. Am. Ceramic Soc., i, 1918, p. 

Additional papers will be found in the Transactions of 
the Ceramic Society. 

Clay-ironstone. A term applied to sheet-like deposits 
of concretionary masses of argillaceous siderite ; 
associated with carbonaceous strata and particu- 
larly with the Coal Measures. 

Clay Rock. A term sometimes applied to indurated 

Clay-slate. A variety of slate, the cleavage planes of 
which are free from the lustre found in slates that 
have attained a more crystalline condition, and 
thus approach phyllite. The term also distin- 
guishes argillaceous slates from those derived from 
volcanic ash. 

Claystone. An obsolete term for an altered felspathic 
igneous rock, in which the whole rock or the 


groundmass has been reduced to a compact mass 
of earthy or clayey alteration products. 

Clay-with-FlintS, \Vhitaher, 1861. A deposit of 
mixed chalk-flints and clay that lies directly on the 
Chalk in many areas, and is often seen in pot-holes 
or pipes. It is usually ascribed to the effect of 
solution-weathering on chalk, but in many cases 
there may be an additional admixture of Tertiary 
materials. The clay is reddish or brown, very 
tenacious, and often nearly black at the base of the 
deposit, becoming- lighter and more sandy higher 
up. Unfortunately the term has been loosely 
applied to almost all the clay-flint drift deposits 
that rest on the Chalk. 

W. Whitaker : Mem. Geol. Surv. (Geology of London), Vol. 
i, 1889, p. 281. 

A. J. Jukes-Browne : Q.J.G.S., Ixii, 1906, p. 132. 

R. L. Sherlock A. H. Noble : Q.J.G.S., Ixviii, 1912, p. 199. 

G. Barrow : Prof. Geol. Assoc., xxx, 1919, p. 23. 

Cleavage. (a) The property of minerals, due to their 
atomic structure, whereby they can be readily 
separated along planes parallel to certain possible 
crystal faces, (b) The property of rocks such as 
slates, which have been subjected to orogenic pres* 
sure, whereby they can be split into thin sheets, the 
plane of cleavage being at right angles or inclined 
to the direction in which the pressure was applied, 
according to the effects produced by shearing- 
stress during the process. 

A. Harker : Re-p. Brit. Assoc., 1885, p. 837. 

G. F. Becker : Journ. Geol., vi, 1896, p. 429. 

C. K. Leith : Structural Geology, 1914, p. 84. 

Coagulation. A term applied to the process whereby 
a homogeneous suspension of a colloidal substance 
in a liquid settles down as a gelatinous mass ; i.e., 
the process whereby a sol passes into a gel. The 
corresponding change in the case of a suspension 
of minute granular material is termed floculation. 
H. F. Ashley: U.S.G.S. Bull. 388, 1909, p. 15.' 


Coal. A general name applied to black carbonaceous 
deposits, derived from accumulations of vegetable 
debris which have been compacted by diagencsis 
into firm brittle rocks exhibiting" a dull or shining 

E. C. Jeffrey : Journ. Geol., xxiii, 1913, p. 218. 

I). White & R. Thiessen : U.S.A. Bureau of Alines, Bull. 38, 


A. Strahan & W. Pollard : Mem. Geol. Surv. (Coals, S. 

Wales), 1915. 

W. Lomax : Trans. Inst. Min. Eng., liii, 1917, p. 137. 
G. Hicklirig : Manchester Geol. and Min. Soc., 1918. 
Marie C. Stopes & R. V. Wheeler : The Constitution of Coal, 

Marie C. Stopes : Proc. Roy. Soc. B., xc, 1919, p. 472. 

Coal-balls. -- Concretions of mineralised plant-debris 
occurring in certain coal-seams. 

Marie C. Stopes & D. M. S. Watson : Phil. Trans. Roy. Soc. 
B., cc, 1908, p. 167. 

Coefficient of Acidity, Vogt. The figure expressing 
the following ratio, calculated from the molecular 
proportions of the constituents of a rock or slag 

Number of atoms of oxygen in SiO z . 
Number of atoms of oxygen in the basic oxides. 

Cognate Inclusions, Harker, 1900. A term applied 
to xenocrysts or xenoliths occurring in an igneous 
rock to which they are genetically related ; = en- 
claves homceogenes autoliths. 
A. Harker : Journ. Geol., viii, 1900, p. 389. 

Cokeite, Lacroix, 1910. Natural coke formed by the 
action of magmas on coal, or by natural combus- 
tion of coal in mines. 
A. Lacroix : Min. de la France, iv, 1910, p. 648. 

Collobrierite, Lacroix, 1917. -- A metamorphic rock 
composed of grunerite, fayalite, garnet, and mag- 
netite. (Collobrieii, France.) 

A. Lacroix : Bull. Soc. franf. Min., xl, 1917, p. 62. 

Colloids. Microheterogeneous substances composed 
of two phases, one of which is dispersed through 
the other; e.g., a jelly in which one phase forms a 


continuous cellular framework, while the other, a 
liquid, occupies the pores. 

Dispersed systems may be molecular, colloidal, 
or coarse ; colloidal systems are denned as those in 
which the diameters of the dispersed particles lie 
between i/x/z and ioo/z/j, (i.e., 1/1,000,000 mm. and 
i/ 10,000 mm.), and they are distinguished from 
molecular solutions by not dialysing, and from 
coarse dispersions by the fact that their individual 
particles cannot be distinguished microscopically. 
Liquid colloids are known as sols, and their coagu- 
lation products as gels. Coagulation is the result 
of a decrease in the degree of dispersion ; peptisa- 
tion that of an increase in the degree of dispersion. 
The following table gives examples of different 
types of dispersed systems : 

s = solid "\ ,. j (S = solid. 






s + S 

Solid inclusions 

Blue rock-salt 

Solid solutions. 

s + L 
s + G 

in minerals. 
Dust, volcanic 

(Nain NaCl). 



1 + S 
1 + L 

Liquid inclusions 
in minerals. 


Water of crystal- 

1+ G 



g + s 

Gas inclusions 
in minerals. 

Occluded gases. 

Adsorbed gases. 

g + L 
g + G 


Colloid foams. 


H. E. Ashley : U.S.G.S. Bull. 388, 1909. 

A. F. Rogers : Journ. Geol., xxv, 1917, p. 515. 

W. Ostwald (trans, by M. H. Fischer) : Theoretical and 

Applied Colloid Chemistry, 1917. 
E. Hatschek : Introduction to the Physics and Chemistry of 

Colloids, 1918. 


Colour Ratio, Shand, 1915. The ratio of felsic (light) 
to mafic (dark and heavy) minerals in an igneous 
rock, which thus accurately expresses the leuco, 
meso-, or melano-cratic character of the rock. 
S. J. Shand : Journ. GeoL, xxiv, 1916, p. 403. 

Columnar Structure. A structure found in lava flows, 
sills, and dykes, and most characteristically deve- 
loped in basaltic rocks, due to the regular develop- 
ment of prismatic joints that break up the rock 
into parallel columns, the sides of which average 
six in number. Analogous prismatic structures 
sometimes occur in rocks other than igneous. 
T. G. Bonney : Q.J.G.S., xxxii, 1876, p. 140. 
E. M. Kindle : GeoL Surv. Canada, Mus. Bull. 2, 1914, 

P- 35- 

R. B. Sosman : Journ. GeoL, xxiv, 1916, p. 215. 
C. Dauzere : C.R. clxix, 1919, p. 76. 

Comagmatic, Washington, 1906. A term applied to 
igneous rocks (or to the district in which they 
occur) characterised by chemical and mineral pecu- 
liarities which point to consanguinity or com- 
munity of origin. The term Comagmatic Region 
according to Washington is wider than Petrogra- 
phical Province (Judd), since " province " implies 
that the area is part of a larger one, and " petro- 
graphical " does not include petrological charac- 
ters and relations. 

H. S. Washington : Carnegie Inst. Wash., Pub. 57, 1906, 
p. v. 

Comendite, Bertolio, 1895. An alkaii-rhyolite con- 
taining soda-pyroxenes and/or soda-amphiboles. 

(Comende, Sardinia.) 
G. T. Prior : Min. Mag. y xiii, 1902, -p. 242. 

Complementary Dykes, Brdgger, 1894. Associated 

dykes (or other minor intrusions) composed of 
different but related rocks regarded respectively as 
hucocratic and melanocratic differentiation pro- 
ducts from a common magma (e.g. , aplites and 
lamprophyres ; bostonite and camptonite). 
VV. C. Brogger : Q.J.G.S., 1, 1894, p. 31. 


Component. In the phase rule this term denotes each 
of the integral parts (independent molecular species 
not connected by a chemical equation), of which a 
system is composed, and in terms of which the 
system may be described (e.g., the system CaO, 
A1 2 3 , Si0 2 ). 

Composite DykCJS, Judd, 1893. Dykes consisting of 

two or more injections of magmas having different 

compositions. The term composite is similarly 

applied to sills, laccoliths and other intrusions. 

Mem. Geol. Surv. Scot., 53 (Ben Nevis and Glen Coe), 1916, 

P- M4- 
A. Harker : Mem. Geol. Surv. Scot. (Tert. Ig. Rocks Skye), 

1904, p. 197. 
W. R. Smellie : Trans. Geol. Soc. Glasgow, 1913, p. i. 

Composite Gneiss. Gneisses produced by the inti- 
mate association, with or without molecular inter- 
mixture, of two different materials, the one (gene- 
rally a granitic magma) having been injected into 
the other (e.g., along the parting planes of a 
G. A. J. Cole : Proc. Roy. Irish Acad., xxiv, 1902, p. 203. 

Concretions. Nodular or irregular concentrations of 
certain authigenic constituents of sedimentary 
rocks and tuffs ; developed by the localised deposi- 
tion of material from solution, generally about a 
central nucleus; e.g., septaria, flint, nodules of 
marcasite or iron-pyrites,- loss puppchen, kankar, 

G. F. Becker : U.S.G.S., Mon., xiii, 1888, p. 64. 
R. Delkeschamp : Zeit. f. Prakt. Geol., xii, 1904, p. 289." 
W. A. Richardson: Min. Mag., xviii, 1919, p. 327. 

Cone-in r COne Structure. A concretionary structure 
occurring in marls, ironstones, coals, etc., char- 
acterised by the development of a succession of 
cones one within another, due to radial crystallisa- 
tion about a common axis. 
G. A. J. Cole : Min. Mag., x, 1892, p. 136. 

Conglomerate. A cemented clastic rock containing 
rounded fragments corresponding in their grade 


sizes to gravel or pebbles. Monogenetic and poly- 
genetic types are recognised, according to the uni- 
formity or variability of the composition and 
source of the pebbles. 

G. R. Mansfield : Bull. Museum CQin-p. Zoology Harvard, 

xlix, Geol. Ser., viii, No. 4. 
J. W. Gregory : Geol. Mag., 1915, p. 447. 
W. Deeke : Ber. Naturjor. Gesell., xxii, (i), 1919.' 

Congressite, Adams & Barlow, 1913. A hololeuco- 
cratic coarsely granular igneous rock composed 
mainly of nepheline, with small amounts of soda- 
lite, plagioclase, micas, calcite, and titanoferrite. 

(Congress Bluff, Craigmont Hill, Ontario.) 
F. D. Adams & A. E. Barlow : Cong. GeoL Inter., xii, 

Guide 2, 1913, p. 96. 

Connate, Lane, 1908. A term applied to waters (and 
extended to include CO 2 in limestones, and other 
volatile materials) buried with exogenetic forma- 
tions and volcanic rocks, and remaining stagnant 
except as they are liberated by diagenesis or meta- 
A. C. Lane : Bull. Geol. Soc. Am., xix, 1908, p. 502. 

Consanguinity, Iddings, 1892. A term implying 
" blood relationship," or community of origin, in 
the rocks of a single volcanic or petrological dis- 
trict or province, and revealed by common pecu- 
liarities of mineral and chemical composition, and 
often also of texture. Cf. Petro graphical Province. 
J. P. Iddings : Bull. Phil. Soc. Wash., xii, 1892, p. 89. 

Consertal, C.I.P.W., 1906. A term applied to equi- 
granular texture, when irregularly-shaped crystals 
closely interlock without interstitial spaces. 
C.l.l'.W. : Jouru. Geol., xiv, 1906, p. 703. 

Contact (or Local) Metamorphism. Metamorphism 

genetically connected with the intrusion (or extru- 
sion) of magmas, i.e., the alteration of rocks re- 
ferred to their contact with or proximity to, a body 
of igneous rock. It is probable that in most cases 
of contact metamorphism the depth at which 
alteration took place was moderate, whereas in 

J v. 


regional metamorphism (also in part due to mag- 
matic transfer of heat) the depth was greater. Cf. 
exomorphic and endomorpliic metamorphism. 

Mems. Geol. Surv. (Silurian Rocks, Britain), I, 1899, p. 634; 
(Ben Nevis and Glen Coe), 1916, p. 187 ; (North-West High- 
lands), 1907, p. 453. 

[. M. Clements : Am. Journ, Sci., vii, 1899, p. 81. 

r . M. <Goldschmidt : Die Kontakt Met am or -phase itn Kris- 
tianiagebiel, 1911. 

Contemporaneous. A term applied to interbedded 
volcanic rocks (contrasting them with sills of later 
date than the enclosing rocks) ; to segregation 
veins and patches (cf. schlieren) in bodies of ig- 
neous rocks ; to dolomites produced from lime- 
stones soon after the deposition of the latter ; and 
generally, to all rocks and facies developed while 
the processes of formation of the enclosing rocks 
were still in operation. 

Convection. - - The internal circulation within a fluid 
mass set up by differences of density in different 
parts of the mass owing to changes in temperature 
or phase. For the application to magmas, see 
F. F. Grout : Journ. Geol., xxvi, 1918, p. 481. 
C. H. Desch : Journ. Inst. Metals, xi, 1914, p. 77. 

Coppaelite, Sabatini, 1903. -- A porphyritic volcanic 
rock composed of phenocrysts of augite in a holo- 
crystalline groundmass of pyroxene, melilite, 
phlogopite and small amounts of perovskite and 
apatite. (Coppaeli di Sotto, Umbria.) 

Coprolite. The fossilised excrement of fishes, reptiles 
and mammals. As these remains are largely com- 
posed of calcium phosphate, the term applied to 
them has been commercially extended to include 
phosphatic nodules. 

Coquina. A loosely cemented fragmental shelly lime- 
stone occurring in Florida. 

Coral Mud and Sand. Deposits formed around coral- 
islands and coasts bordered by coral-reefs, contain- 
ing abundant fragments of corals. Near the reefs 
the grade sizes are relatively coarse, and the 


deposit is described as coral-sand, whereas further 
out, the grades become gradually finer until the 
material is a coral-mud. 

J. Murray & A. F. Renard : " Challenger " Rep. (Deep Sea 
Deposits), 1891, p. 244. 

Cordierite-anthophyllite Rock, Eskola, 1914. A 

pneumatolytic-metamorphic rock consisting essen- 
tially of anthophyllite (as radiating bunches or irre- 
gularly distributed prisms) and cordierite. Other 
minerals, such as biotite, garnet, quartz, plagio- 
clase and magnetite, may be present in varying 
amounts, and by increase in plagioclase the type 
passes into plagioclase-gneiss. 

P. Eskola : Bull. Comm. Geol. Finlande, 40, 1914, pp. 169, 
187, 252. 

Cordierite-norite, Lacroix, 1898. A term applied to 
endomorphic varieties of norite containing cor- 
dierite. Cf. Mtiscovadite. 

A. Lacroix : Butt. Serv. Carte Geol. France, No. 67, x, 1898- 

W. R. Watt : Q.J.G.S., Ixx, 1914, p. 285. 

For Cordierite in general, see 

J. J. H. Teall : Proc. Geol. Assoc., xvi, 1899, p. 62. 

Cornstone. A term applied to the concretionary and 
other limestone masses associated with the Old 
. Red and the New Red Sandstone formations. 
Their presence increases the fertility of the soil 
derived from the formations in which they occur, 
and hence the name. 

Cornttbianite, Boase, 1832. -- A term applied to 
finely granulose rocks of horny aspect (hornfels), 
formed by contact metamorphism, and consisting 
of micas, quartz, and felspar. Cf. Leptynolite. 

( Cornubia = Cornwall. ) 
T. G. Bonney : Q.J.G.S., xlii, 1886, p. 104. 
W. Salomon : Cong. Geol. Inter. C.R., viii (Paris, 1900). 
1901, p^. 343. 

Corona (Coronite, Brdgger). A term applied to zones 
of radially-arranged minerals (e.g., of pyroxene 
amphibole, garnet, etc.) that occur around olivine 
or hypersthene in certain gabbros, norites- and re- 


lated rocks. They may be metamorphic reaction 
rims, or due directly to the order of crystallisation, 
and thus of igneous origin. It has been suggested 
by Bonney that the term Kelyphitic rim be 
restricted to occurrences of secondary origin, leav- 
ing Corona for those that are primary. 

Corrosion. The modification of phenocrysts or 
xenoliths, etc., by the solvent action* upon them of 
the residual magma in which they are contained. 
The same term (corrasicn of some American 
authors) connotes the vertical excavation of the 
land by rivers and glaciers. 
P. Eskola : Bull. Comm. Geol. Finlande, 40, 1914, p. 22. 

Corsite, Collomb, 1853. - - A well-known variety of 
orbicular diorite or hornblende-gabbro occurring in 
Corsica =Napoleonite. 

Cortlandtite, Williams, 1886. Hornblende-peridotite 
= Hudsonite. The type variety contains horn- 
blende in large crystals, with poikilitically-in- 
cluded crystals of olivine. 

(Cortlandt, New York.) 
G. S. Rogers : Ann. N. York Acad. Set., xxi, 1911, p. n. 

Corundolite, Wadsworth, 1891. A systematic term 
proposed for emery-rock. 

Country Rock. -- A general term for the rock sur- 
rounding and penetrated by mineral veins ; some- 
times used in a wider sense for the rocks invaded 
by igneous intrusions. 

Covite, Washington, 1900. A somewhat melanocratic 
variety of nepheline-syenite, in composition falling 
between the latter and shonkinite. 

(Magnet Cove, Arkansas.) 
H. S. Washington : Journ. Geol., ix, 1901, p. 612. 

Craiglockhart Basalt, Hatch, 1892. -- A type of the 

Scottish Carboniferous basalts ; characterised by 
the presence of conspicuous phenocrysts of olivine 
and augite in a fine-grained basaltic groundmass. 
E. B. Bailey : Mem. Geol. Surv. Scot. (East Lothian), 1910, 
p. 118. 


Craigmontite, Adams & Barloiv. -- A leucocratic 
facies of nepheline-syenite, containing in order of 
abundance, nepheline, oligoclase, and muscovite, 
with small amounts of calcite, corundum, biotite 
and magnetite. (Craigmont Hill, Ontario.) 

F. D. Adams & A. E. Barlow : Geol. Surv. Canada Mem., 
6 (Pub. No. 1,082), 1910, p. 313. 

Crinanite, Flett, 1911. A variety of olivine-analcite- 
dolerite, containing purple augite, and char- 
acterised by well-developed ophitic texture. 

(Loch Crinan, Argyll.) 
Mem. Geol. Surv. Scot. (Colonsay), 1911, p. 35. 

Cromaltite, Shand, 1906. An alkali pyroxenite, con- 
taining aegirine-augite, melanite and biotite. 

(Cromalt Hills, Assynt.) 

, S. J. Shand : Trans. Edin. Geol. Soc., ix, 1910, p. 394. 

Crush-breccia, Bonney. A cataclastic breccia formed 
in or nearly in situ by mechanical fragmentation. 

Crush-conglomerate, Lamplugh, 1895. A cataclastic 
conglomerate formed by mechanical fragmentation 
and friction, due to earth-stresses. 

G. W. Lamplugh: Q.J.G.S., li, 1895, p. 563. 

Cryptocrystalline (Microcryptocrystalline of some 
American authors). A term implying that a rock 
or groundmass is composed of a crystalline aggre- 
gate that can only be recognised as such by its 
appearance in thin section between crossed nicols ; 
individual minerals not being directly determinable. 

Cryptographic, Harker, 1895. A texture, often 
radial, due to the intergrowth of quartz and felspar 
on so fine a scale that the individual component 
minerals cannot be clearly resolved under the 
microscope ; a cryptocrystalline granophyric 

Crystal. A body, generally solid, but not necessarily 
so, whose, component atoms are arranged in 
definite space lattices, crystal faces being a com- 


monly developed outward expression of the 
periodic arrangement of atoms. 
W. H. and W. L. Bragg : X-Rays and Crystal Structure, 

I 9 I 5- 

F. E. Wright : Journ. Wash. Acad. Sci., vi, 1916, p. 326. 

Crystalline Limestone. -- A general term for meta- 
morphosed limestones, the mineral composition 
depending on the character of the original lime- 
stone, the thermo-dynamic conditions under which 
the metamorphism was effected, and the amount 
and composition of material (if any) introduced 
from external sources. See calciphyre, cipolino, 
marble, ophicalcite, predazzite, etc. A limestone 
recrystallised by diagenesis is described as recrys- 

A. K. Coomaraswamy : Q.J.G.S., li, 1902, p. 399; lix, 1903, 
p. 91. 

J. J. H. Teall: Mem. GeoL Stirv. (N.W. Highlands), 1907, 
p. 41. 

A. S. Eakle : Butt. De-pt. Geol. Univ. California, x, 1917, 
P. 327- 

Crystalline Schist. See Schist. 

For References see under Metamorphism. 

Crystal linity. A term applied to the degree of 
crystallisation exhibited by an igneous rock ; ex- 
pressed by terms such as holo crystalline, hypo- 
crystalline, holohy aline, etc. 

Crystallisation. - The process whereby crystalline 
phases separate from a fluid, viscous, or dispersed 
state (gas, liquid solution, or rigid solution). 

G. F. Becker & A. L. Day : Journ. GeoL, xxiv, 1916, p. 313. 
F. E. Wright : Journ. Wash. Acad. Sci., vi, 1916, p. 326. 

Crystallite, Vogelsang, 1870. - - A general term for 
minute bodies without reaction on polarised light, 
occurring in glassy igneous rocks : e.g., globulite, 
longulite, margarile, trichite, and other forms of 
incipient crystallisation that cannot be referred to 
definite mineral species. 
F. Rutley : Min. Mag., ix, 1891, p. 261. 
C, H. Desch : Journ. Inst. Metals, xi, 1914, p. 65. 


Crystalloblastic, Becke, 1903. A term applied to the 
textures of metamorphic rocks due to recrystallisa- 
tion under conditions of high viscosity and 
directed pressure, in order to distinguish them 
from the textures of igneous rocks, which are due 
to the successive crystallisation of- minerals under 
conditions of relatively low viscosity and nearly 
uniform pressure. 

F. Becke : Cong. Geol. Inter. C.R., ix, 1903, p. 553. 

U. Grubenmann : Die Kristallinen Schiefer, I, 1904. 

F. L. Stillwell : Aust. Ant. Ex-ped. Sci. Reft. A, iii, T (i) 
(Met. Rocks, Adelie Land), 1918, p. 40. 

Crystal Tuffs, Cohen, 1871. - - Volcanic tuffs, which 
are largely composed of crystal fragments. Cf. 
vitric and lithic tuffs. 
L. V. Pirsson : Am. Journ. Sci., xl, 1915, p. 191. 

Cltcalite, Rolle, 1879. - - A variety of diabase char- 
acterised by abundant chlorite and passing locally 
into chlorite-schist. (Rhsetic Alps.) 

Culm. A vernacular term variously applied according 
to the locality, to carbonaceous shale, or to fissile 
varieties of anthracitic coal. The term has also a 
definite stratigraphical meaning for beds of 
Pendleside and Westphalian age. 

Cumber landite, Wadsworth, 1884. A phanerocrys- 
talline rock composed of ferriferous olivine, 
ilmenite and magnetite, with small amounts of 
labradorite and spinel. 

(Iron Mine Hill, Cumberland, Rhode I.) 

Cumbraite, Tyrrell, 1917. A porphyritic rock, con- 
taining phenocrysts of bytownite-anorthite in a 
groundmass of labradorite,, enstatite-augite and 
abundant glass ; and in chemical composition cor- 
responding to andesite rather than to basalt. 

(Great Cumbrae, Firth of Clyde.) 
G. W. Tyrrell : Geol. Mag., 1917, p. 306. 

Cumulite, Vogelsang, 1872. A term applied to cloudy 
aggregates of globulites occurring in vitreous 


F. Rntley : Min. Mag., ix, 1891, p. 261. 


Cumulophyric, C.I.P.W., 1906. A term applied to 
glomeroporphyritic texture in the widest sense, 
i.e., when the clusters of crystals forming com- 
posite phenocrysts are not necessarily aggregates 
of the same mineral. 
C.T.P.W. : Joitrn. Geol., xiv, 1906, p. 703. 

Cumulose Deposits, Merrill, 1897. - - Sedentary 
accumulations of carbonaceous matter, with very 
little detrital sediment, e.g. , peat, swamp-soil. 

Cup-and-ball Structure, A cross jointing of columnar 
igneous rocks, in which one face of the joint is 
concave and the other convex ; as in the columns 
of the Giant's Causeway. 

Cupola, Daly, 1911. A dome- or boss-like protrusion 
from the body of a batholith, forming a con- 
spicuous irregularity in its roof. 

Current- or Cross-bedding. A structure of sedi- 
mentary rocks, generally arenaceous, in which the 
planes of deposition, as shown by the arrangement 
of the grains in successive layers, lie obliquely to 
the planes separating the larger units of stratifica- 
tion. The structure is commonly developed in 
aeolian, deltaic and torrential deposits, each of 
which has its own distinctive characters. 

Cuselite, Rosenbvsch t 1887. A term applied to leuco- 
cratic varieties of biotite-augite-porphyrite con- 
taining abundant phenocrysts of andesine and few 
of the mafic minerals, in a felspathic groundmass. 

(Cusel, Saar Basin.) 


Dacite. Quartz-andesite. According to the composi- 
tion of the plagioclas-e, three different types of 
dacite are distinguished by Iddings : Ungaite 
(oligoclase), Shastaite (andesine), and Bandaite 
(labradorite). The last of these would generally 
be regarded as a variety of quartz-basalt. 
H. H. Robinson: U.S.G.S., Prof. Pa$., 76, 1913, p. 114. 


Dacitoid, Lacroix, 1919. A volcanic rock having the 
chemical composition of dacite but free from 
modal quartz. 
A. Lacroix : C.R., xlxviii, 1919, p. 297. 

Dactylitic, Sedefholm, 1916. A textural term applied 
to finger-like projections from a continuous crystal, 
the fingers (e.g., of biotite) and the intercalated 
mineral between them (e.g. , of quartz) together 
forming a symplektite, q.v. 

J. J. Sederholm : Bull. Comm. Geol. Finlande, No. 48, 
1916, Figs. 32-4, PI. vi. 

Dactylotype, Shand, 1906. A textural term applied 
to the intergrowth of sodalite with orthoclase in 
borolanite and its associates ; the sodalite has been 
altered to pinitic mica and appears in thread-like or 
vermicular aggregates closely packed in a matrix 
of orthoclase. 
S. J. Shand : Trans. Edin. Geol. Soc., ix, 1910, p. 387, PI. 39. 

Dahamite, Pelikan, 1902. A variety of paisanite 
characterised by the presence of abundant albite. 

(Dahamis, Socotra.) 

Dalmeny Basalt, Hatch, 1892. A type of the Scottish 
Carboniferous basalts ; characterised by the abund- 
ance of microphenocrysts of olivine, augite and 
plagioclase being restricted almost always to the 
J. D. Falconer : Irans. Roy. Soc. Edin., xlv, 1906, p. 133. 

Damouritisation, Lacroix, 1896. The process where- 
by the aluminous silicates (felspars, etc.), of a rock 
are transformed into damourite (a variety of mus- 

A. Lacroix : Min. de la France, n, 1896, p. 41. 

Davainite, Wyllie & Scott, 1913. A rock consisting 
essentially of brown hornblende which is para- 
morphic after pyroxene, the amount of other 
minerals, such as felspar, being small. 

(Garabal Hill.) 

B. K. N. Wyllie & A. Scott : Geol. Mag., 1913, p. 499. 



Dedolomitisation, Teall. -- A process whereby a 
dolomite, during metamorphism, loses its content 
of magnesium carbonate, the magnesium remain- 
ing as oxide or hydroxide (e.g., in pencatite) Qt 

as a silicate (e.g., in forsierite marble, ophicalcite, 
etc.). It is not desirable to extend the term, as 
has recently been suggested, to include the re- 
moval of dolomite mechanically. 

J. J. H. Teall : Geol. Mag., 1903, p. '513. 

A. Harker : Mem. Geol. Si:rv. (Tert. Ig. Rocks Skye), 1904, 
p. 144. 

J. J. H. Teall: Mem. Geol. Siirv. Scot. (X.\V. Highlands), 
1907, p. 453. 

F. H. Hatch & R. H. Rastall : Q.J.G.S., Ixvi, 1910, p. 507. 

T. Crook : Geol. Mag., 1914, p. 339. 

of Freedom. The number of physical condi- 
tions, including temperature, pressure, and con- 
centration, that can be varied independently in a 
system without destroying a phase. 

Dellenite, Brogger, 1896. - - A volcanic rock inter- 
mediate between rhyolite and dacite, i.e., contain- 
ing both orthoclase and oligoclase-andesine ; = 
quartz-latitc = quartz-trachyaiidesite. 

(Lake Dellen, Sweden.) 

Density. The density of a substance is the weight (ex- 
pressed in grams) of unit volume (one cubic centi- 
metre) of the substance at 4 C. Cf. Specific 

A. L. Day et aliter : Am. /. Sci., xxxvii, 1914, p. i. 

A. Holmes : PetrograpJric Methods and Calculations, 1920. 

Denudation, Poullet-Scrope, 1825. - - The sum of the 
processes that result in the wearing down of the 
surface of the earth. The term is wider in its 
scope than erosion, the restriction proposed by 
Lyell (limiting it to the action of running water) 
not having been generally adopted. 

J. W. Gregory : Geog. Journ., xxxvii, 1911, p. 189. 

J. W. Evans : Proc. Geol. Assoc., xxiv, 1913. p. 241 ; xxv, 
1914, p. 229. 


Derivate, Forbes, 1867. A general term for "sedi- 
mentary " rocks derived from the products of 
destruction of primary rocks. Cf. Ingenite. 

Dermolith, Jag gar, 1917. A term, meaning " skin- 
stone," applied to ropy-lava or pahoehoe-lava. 
T. A. Jaggar : Jour. Wash. Acad. Sci., vii, 1917. 

Desmosite, Zincken, 1841. A contact metamorphosed 
shale or slate differing from spilosite by having a 
banded structure. 

Detritus. -- Fragmented (epiclastic) material, such as 
sand and mud, derived from older rocks by dis- 
integration. The deposits produced by the 
accumulation of detritus constitute the detrital 

Deuteric, Sederholm f 1916. A term applied to altera- 
tions in an igneous rock produced during the later 
stages, and as a direct consequence, of the con- 
solidation of the magma of the rock. (Cf. Paulo- 
post.) The term discriminates such alterations 
from the more strictly secondary changes due to a 
later period of alteration. 

j. J. Sederholm : Bull. Couim. Geol. Finlande, No. 48, 1916, 
p. 142. 

DeuterogeriOUS, Naumann, 1858. A group name for 
"derived" rocks; used more definitely by Rene- 
vier, 1880, for sedimentary rocks of mechanical 

Deuteromorphic, Loewin3Qn-Lessing J 1897. A general 
term applied to crystals to indicate that their 
shapes have been acquired or modified by the action 
of mechanical or chemical processes on the forms 
which they originally possessed. Deuteromorphic 
forms are described as tectomorphic when the 
modifications are due to magmatic corrosion ; as 
lytomorphic, when due to aqueous solutions ; as 
schizomorphic, when due to cataclastic processes ; 
as clastomorphic, when due to denudation as in the 
rounded or angular grains of a detrital sediment ; 
and as neonwrphic when any one of the preceding 


types has been regenerated by zones of secondary 
growth in crystalline continuity. 

Devitrification. The process by which glass (natural 
or artificial) develops a minutely crystalline or 
lithoidal texture, and becomes microfelsitic or 
microspherulitic. Devitrification is an expression 
of solid diffusion, promoted by crystal forces so 
long as the latter are not inhibited by internal 

T. G. Bonney & J. Parkinson : Q.J.G.S., ix, 1903, p. 429. 

N. L. Bowen : Journ. Am. Ceramic Soc., ii, 1919, p. 261. 

DeVOnite, Johannsen, 1910. A variety of porphyritic 
dolerite characterised by phenocrysts of plagio- 
clase rich in potassium. (Mt. Devon, Mass.) 

Diabase, Brongniart, 1807. This term originally de- 
noted rocks that were later recognised by Haiiy 
as diorites. (Conversely, in many of the older 
geological maps of Ireland, rocks are named 
diorite that would now be called diabase.) For a 
time the term diabase was applied to pre-Tertiary 
dolerites, and since, especially in Britain, such 
rocks are frequently altered, the term has come to 
mean an altered dolerite in which the felspars are 
saussuritised or albitised, or the pyroxenes more 
or less replaced by hornblende or chlorite. Ger- 
man and most American authors, however (follow- 
ing Rosenbusch), use diabase in a sense synony- 
mous with the British usage of dolerite. 

Diablastic, Becke, 1903. See Sieve Texture. 

Diagenesis, Gumbel, 1888. A term denoting the sum 
of the successive changes which take place in 
exogenetic rocks as a result of continued sedi- 
mentation above them, or of the percolation of 
ground-waters through them; e.g., consolidation, 
development of lamination by increase of vertical 
pressure due to the superincumbent load, and 
cementation and recrystallisation due to seasonal 


and other regular changes in water content and 
temperature of a normal exogenetic character. 

E. Andree : Geol. Rund., iii, 1912, p. 324. 

W. Deeke : Ber. Naturfor. GeselL, xxii, (i), 1919. 

Diallagite, Des Cloizeaux, 1863. -- A rock composed 
almost wholly of diallage. Small amounts of 
other pyroxenes, hornblende, pleonaste, or garnet 
may be present. 

Diamagnetism, Faraday, 1845. A property of certain 
substances -- essentially different from ferro- 
magnetism and paramagnetism in virtue of 
which, when placed in a non-uniform magnetic 
field, they tend to move towards the weakest part. 
Unlike ordinary magnetic bodies the molecule has 
either no inherent polarity or has a balanced 
polarity. In a magnetic field the induced polarity 
leads to repulsion, arid diamagnetic susceptibility 
is therefore negative. Cf. Paramagnetism. 
T. Crook : Science Progress, No. 5, 1907, p. 30. 

DiaschistlC, Brogger, 1896. A term applied to those 
rocks of minor intrusions which appear to be 
respectively melanocratic or leucocratic dif- 
ferentiates from a common magmatic source. 

Diatomite, Diatomaceous Earth. A pulverulent 

siliceous deposit formed by the accumulation of the 
frustules of diatoms in lakes or swamps ; = Tripoli 

= Kieselguhr. 

Diatom Ooze, Murray, 1873. A deep-sea deposit, re- 
sembling flour when dry, largely composed of the 
frustules of diatoms, and containing a small but 
variable proportion of calcareous organisms and 
mineral particles. 

J. Murray & A. F. Renard : " Challenger " Rep. (Deep Sea 
Deposits), 1891, p. 208. 

Diatreme. - - A general term for volcanic pipes and 
vents drilled through the enclosing rocks by the ex- 
plosive energy of gas-charged magmas. 
W. Branca : Schwaben 125 Vulcanembryonen , Stuttgart, 


Differential Pressure. See Directed Pressure. 

J. Johnston & P. Niggli : Journ. GeoL, xxi, 1913, p. 614. 

Differentiated (S/77, Dyke, TMccoHth, Batholith, etc.}. 
A term applied to major and minor intrusions 
that are built up of two or more rock-types that 
have developed in situ by differentiation from a 
common rnagna. 

R. A. Daly : Igneous Rocks and their Origin, 1914, p. 229, 
and Table xiv, p. 230. 

Differentiation. - - A general term for the processes 
whereby different types of igneous rocks, which 
may or may not form parts of the same mass, are 
produced from .a common magmatic source ; the 
processes involved may be molecular, or the 
separation of immiscible liquids, or the separation 
of residual liquids from crystals already formed ; 
and the interactions between units of differentia- 
tion formed at one time or place with those formed 
at other times or places must also be considered, 
and especially in relation to thermo-dynamic con- 
ditions and the presence of volatile fluxes. 

W. C. Brogger : Eru-ptivgest. Kristiania, iii, 1898, p. 334. 

See also S. J. Shand : An Introduction to Petrology, etc. 
(Royal Scottish Museum, Edinburgh), 1909, p. 43, for 
a summary account of Brogger's work and its results. 

H. S. Washington : Journ. GeoL, ix, 1901, p. 645. 

A. Harker : Nat. Hist. Ig. Rocks, 1909, p. 309. 

Cong. GeoL Inter. C.R.. xii (1912), 1913, p. 189. 

H. S. Jevons : Journ. Roy. Soc. N.S.W., xlvi, 1913, p. 112. 

N. L. Bowen : Am. Journ. Sci., xxxix, 1915, p. 175 ; xl, 
1915, p. 161. 
- Joi4rn. GeoL, Supplement to xxiii, 1915, p. 3. 

A. Holmes : Q.J.G.S., Ixxii, 1917, p. 271. 

R. A. Daly: Journ. GeoL, xxvi, 1918, p. 115. 

F. F. Grout : Journ. GeoL, xxvi, iqrS, p. 626. 

H. H. Read : GeoL Mag.. 1919, p. 368; 1920, p. 86. 

N. L. Bowen : Journ. GeoL, xxvii, 1919, p. 393. 

Diffusion. The permeation of one substance through 
another ; such as gas through gas, liquid or solid ; 
solute through solvent, liquid through liquid or 
solid, and finally solid through solid. The pres- 


sure corresponding to that exerted by dissolved 
material in its diffusion from a more concentrated 
to a less concentrated part of a solution is called 
Osmotic pressure. 

R. F,. Liesegang : GeologiscJie Diffttsionen, 1913. 

C. H. Desch : Re-p. Brit. Assoc. (Dundee, 1912), 1913, p. 348. 

C. E. Van Orstand & F. P. Dewey : U.S.G.S., Prof. Pa-p., 

95, iQ^. P- 8 3- 

Diluvium. An old term by which the older Quarter- 
nary or Pleistocene deposits were described in con- 
tradistinction to the young-er Quarternary or 
Recent deposits laid down by rivers (alluvium). 
The term diluvium refers to the Deluge of Noah to 
the action of which the deposits were originally 
supposed to be due. 

Diogenite, Tschermak, 1883. - - An achondritic 
meteorite composed essentially of bronzite with 
small amounts of oligoclase ; = oHgoclase chlad- 

Diorite. D'Aubuisson, 1819. - A phanerocrystalline 
igneous rock composed of plagioclase (averaging 
andesine, or occasionally oligoclase) and mafic 
minerals such as hornblende, biotite, and augite, 
hornblende being especially characteristic. If 
quartz be present the term qitartz-dioritc is used. 
The term diorite means " a clear distinction " as 
opposed to dolerite, which means " deceptive." 
In Ireland many altered rocks, such as diabase 
and epidiorite, have been described as diorite on 
the older maps. Cf. Laugenite. 

Dipyrisation, Lacroix, 1896, = Scapolitisation. The 

process, sometimes involving pneumatolytic or 
allied agencies, whereby the felspathic constituents 
of a rock are replaced by dipyre or scapolite. 

N. Sundius : Geologie des Kirunagebietes, Upsala, 1915, P- 

A. Lacroix : Bull. Soc. fran$. Min., 1916, p. 74. 

Directed Pressure, Evans, 1919. A term suggested 
in place of the terms " unequal," " non-uniform " 


or " differential " pressure to denote the maximum 
stress-difference acting- on any system, and which, 
unlike hydrostatic or " uniform " pressure 
operates in a definite direction. Thus a compres- 
sion, and in general any natural pressure is resol- 
vable into hydrostatic pressure, and directed 
pressure. The latter can have little effect on the 
properties of liquids beyond causing- them to flow ; 
but acting on solids, it modifies old structures and 
tends to the production of new ones, ranging in 
the case of rocks from mountain building" to 
microscopic granulation., and leading finally to re- 
crystallisation. During- dynamic metamorphism 
the behaviour of crystalline bodies is controlled by 
both the hydrostatic and directed components of 
pressure whereas fluid phases are subject to 
the action of the former component only. Under 
these conditions the melting or volatilisation points 
of solids are lowered, locally and momentarily, and 
thus recrystallisation and diffusion are promoted. 
The study of dynamic metamorphism is essentially 
the study of the modifications effected in rocks by 
directed pressure. 

J. Johnston & P. Niggli : Journ. Geol., xxi, 1913, p. 599. 

J. Johnston : Journ. Geol., xxiii, 1915, p. 732. 

A. Harker : Q.J.G.S., Ixxiv, 1918. p. Ixxvii. 

J. W. Evans : Nature, civ, Oct. and, 1919, p. 106. 

Ditroite, Zirkel, 1866. A variety of nepheline-syenite 
containing sodalite among the felsic constituents, 
and biotite and aegirine-augite among the mafic 
minerals, with zircon and perovskite as note- 
worthy accessories. By Brogger, the term has 
been adopted to include all nepheline-syenites of 
granular texture, as opposed to those of trachytoid 
texture (foyaite). (Ditro, Transylvania.) 

Do-, C.I.P.W., 1902. -- A prefix indicating that one 
factor dominates over another within the ratios 7/1 
an d 5/3 (7 and 1.67); e.g., docalcic, dofemic, 
dosalic, etc. 


Dolerine, Jurine. A variety of talc-schist containing 
felspar and chlorite as the chief varietal minerals. 

(Pennine Alps.) 

Dolerite, Hauy. An igneous rock occurring as minor 
intrusions, consisting essentially of plagioclase 
(not less calcic than labradorite), and pyroxene. 
Olivine-bearing types are distinguished as olivine- 
dolerite. In a general way dolerite is distinguished 
from basalt by its coarser grain and the absence 
of glassy specifically, according to the defini- 
tion of the Comit^ francaise de Petro graphic, 1900, 
by its holocrystalline character and the develop- 
ment of ophitic texture. In practice, however, 
there are many cases in which it is difficult, if not 
impossible, to make an unequivocal choice between 
the terms basalt and dolerite, since there is not, 
and cannot be, any definable line drawn between 
them. As field-terms, however, these names 
are generally restricted to extrusive and in- 
trusive rocks respectively. Many Continental 
and American authors use the term diabase in a 
sense synonymous with dolerite; whereas in 
Britain only altered dolerites are denoted by the 
term diabase. 

S. Allport : Q.J.G.S., xxx. 1874, p. 520. 

J. J. H. Teall : Q.J.G.S., xl, 1884, p. 640. 

A. Harker : Mem. Geol. Surv. (Tert. Tg. Rocks Skye), 1904, 
P- 3*5- 

Dolomite, de Saussure, 1796. A carbonate rock, con- 
sisting predominantly of the mineral dolomite. 

Mem. Geol. Surv. S-pec. Re-p. Mineral Resources, vi, 1918, 
p. 190. 

Dolomite-marble. - - A variety of marble composed 
largely of dolomite, due to the metamorphism of 
dolomite-rock under physical conditions involving 
sufficiently high pressure to inhibit the dissociation 
of the compound CaMg(CO.,) 2 . 
F. H. Hatch & R. H. Rastall : Q.J.G.S., Ixvi, 1910, p. 507. 


Dolomitic Limestone. A limestone containing dolo- 
mite, but in which CaCO, is dominant over 
MgCO v Cf. Magnesian Limestone. 

Dolomitisation. -- A general term for the processes 
whereby dolomite takes the place of CaCO, in 
limestones, the latter thus becoming dolomitic 
limestones, or dolomites. The processes are 
described as contemporaneous when they take 
place shortly after the deposition of the limestone 
concerned, and as subsequent when they occur dur- 
ing some period later than that during which the 
limestones were deposited. 

Re-port of the Coral Reef Committee of the Royal Society, 


F. Steidtmann : Journ. GeoL, xix, 1911, pp. 223, 392. 
R. C. Wallace : Cong. GeoL Inter., C.R., xii (1913), 1914, 

P- 875. 
F. M. Van Tuyl : GeoL Siirv. loiva, U.S.A., vol. xxv, 1916, 

P- 364- 
L. M. Parsons : GeoL Mag., 1918, p. 246. 

Dome. This term is used not only to connote certain 
crystallographic, structural, and geographical 
phenomena, but also to describe at least two dif- 
ferent types of modes of occurrence of igneous 
rocks : It is applied (a) to stocks whose sides 
slope away quaquaversally at low and gradually in- 
creasing angles beneath the invaded formations ; 
and (b) to rounded extrusions of highly viscous 
lava squeezed out from a volcano, and congealed 
above and around the orifice instead of flowing 
away in streams. Portions of older lavas or 
ejectamenta may be elevated by the pressure of 
the new lava rising from beneath. The second 
type of dome is usually distinguished as a volcanic 

A. Lacroix : La montagne Pelee et ses eruptions, 1906, p. 
no; La montagne Pelee a-pres ses eru-ptions, 1908, p. 31. 

S. Powers : Am. Journ. Sci., xlii, 1916, p. 261. 

Domite, von Buck. A general term for the hornblende- 
and biotite-trachytes of the Puy de Dome. Many 


of these are olig-oclase-bearing, and the term has 
therefore come to be applied more specifically to 
olig-oclase-trachytes or trachyandesites. 

A. Lacroix : C.R., cxlvii, 1908, p. 830. 

Drachenfels Trachyte. A type of trachyte containing 
phenocrysts of sanidine and olig-oclase in a ground- 
mass of lath-shaped microlites of orthoclase 
with sparing- biotite, hornblende, and magnetite. 
Dreikanter. A term applied to the three-edged 
faceted pebbles formed by wind action in a dry 
climate,, whether hot (desert) or cold (glacial). 

F. A. Bather : Proc. Geol. Assoc., xvi, 1900, p. 396. 

A. Wade : Geol. Mag., 1910, p. 394. 

J. W. Evans : Geol. Mag., 1911, p. 334. 

J. W. Jackson : Mem. and Proc. Manchester Lit. and Phil 
Soc., 1918, Ixii, No. 9. 

Druse. - - A cavity whose walls are encrusted with 
crystals of the same minerals as those of the en- 
closing- rock. To such cavities and the rocks con- 
taining* them the term drusy is applied. Cf. 
miarolitic. Distinguished from geode by the fact 
that the latter can be separated as a hollow nodular 
secretion consisting- generally of mineral?; different 
from those of the rock in which it occurs. 

Dtimalite, T.oeivinson-Lessing, 1905. - - A varietv of 
trachyandesite. (Caucasus.) 

Dungannonite, Adams & Barlow, 1909. A granitoid 
igneous rock containing-, in order of abundance, 
andesine, corundum, scapolite, micas, and some- 
times a little nepheline. 

(Dung-annon, Renfrew Co., Ontario.) 
F. D. Adams & A. E. Barlow : Geol. Surv. Canada, Mem. 6 
(Pub. No. 1082), 1910, p. 322. 

Dunite, von Hochstetter, 1864. A peridotite consist- 
ing- essentially of olivine, and often containing 
J. M. Bell : Geol. Surv. New Zealand, Bull. 12, 1911, p. 31. 

Dunsapie Basalt, Bailey, 1910. A type of the Scottish 
Carboniferous basalts ; characterised by the pre- 
sence of numerous phenocrysts of plagioclase, 


augite, and olivine, in a normal basaltic ground- 
mass. Cf. Lion's Haunch Basalt. 

E. B. Bailey : Mem. Geol. Surv. Scot. (East Lothian), iqio, 
p. no- 

G. W. Tyrrell : Trans. Geol. Soc. Glasgow, xiv, 10*2, p. 245. 

Dlinstone. (a) A local name for amygdaloidal spilite 

or diabase in the neighbourhood of Plymouth. 
R. H. Worth : Trans. Devon Assoc., xlviii, iqi6, p. 217. 
(b) A local name for certain varieties of magnesian 
limestone in the neighbourhood of Matlock.. 

Durain, Stopes, 1919. A term suggested for the dull, 
hard ingredient of bituminous coal, which occurs 
in bands or lenticles of variable thickness having a 
close, firm, granular texture, generally flecked with 
hair-like streaks of bright coal. Under the 
microscope durain shows amber- to red-tinted 
spores embedded in a dark-grey, nearly opaque 
granular matrix. 
Marie C. Stopes : Proc. Roy. Soc. B., xc, IQIQ, p. 474. 

Durbachlte, Sauer. A melanocratic biotite-syenite. 

(Durbach, Schwarzwald.) 

Dyke. An injected wall-like intrusion, cutting across 
the bedding or other parallel structures of the in- 
vaded formations, and having a thickness narrow 
in proportion to its length. 

Dynamic Metamorphism. The sum of the processes, 

controlled by orogenic movement and differential 
stresses, which were sufficiently powerful under the 
conditions of temperature at which the changes 
took place, to impress a totallv new specific char- 
acter on the rocks affected ; involving marked 
structural changes due to crushing and shearing at 
low temperatures, and extensive recrystallisation 
at higher temperatures. The noteworthy features 
by which dynamic metamorphism is recognised 
become less distinctive at still higher temperatures, 
until, when conditions of extensive fusion are ap- 
proached, at which point directed pressure be- 


comes ineffective, they gradually die away. Cf. 

Piezo 'crystallisation. 

P. Quensei : Bull. Geol. Inst. U-psala, xv, 1916, p. 91. 
R. A. Daly : Bull. Geol. Soc. Am., 28, 1917, p. 395. 
J. J. H. Teall : Proc. Geol. Assoc., xxix, 1918, p. i. 


Eclogite, Haiiy. A granulose rock formed of garnet, 
pyroxene (omphacite) and sometimes amphibole 
(smaragdite), with accessories such as sphene and 
zoisite ; probably derived from gabbros, or rocks of 
corresponding composition, by high temperature 
metamorphism under conditions of high pressure 
and differential stress, or from magmas of cor- 
responding composition by piezocrystallisation. 
T. G. Bonney : Min. Mag., vii, 1886, p. i. 

Edolite, Salomon, 1898. A variety of hornfels con- 
sisting essentially of felspar and mica. Cordierite- 
and andalusite-edolites are recognised. Cf. Avio- 
lite and Astite. (Edelo, Italian Alps.) 

Effusive. A term applied to igneous rocks poured out 
of a vent or fissure, as distinct from those ejected 
or injected. 

Ehrwaldite, Pichler, 1875.* A variety of augitite con- 
taining both rhombic and monoclinic pyroxenes. 


Sjectamenta. A general term for pyroclastic mater- 
ials ejected from a volcanic \ent ; classified by 
Johnstone-Lavis as essential when they consist of 
material directly derived from the magma of the 
eruption ; accessory when they consist of re-ejected 
portions of the volcanic cone; and accidental 
when they consist of older rocks underlying the 
H. J. Johaston-Lavis : Proc. Geol. Assoc., ix, 1886, p. 421. 

Ejected Blocks. A term applied to the larger frag- 
ments of a volcanic breccia, generally derived from 


the internal or subjacent rocks of a volcano, and 
often highly metamorphosed. 

H. J. Johnston-Lavis : Trans. Edin. Geol. Soc., vi, 1893, 
P- 3*4- 

Ekerite, Brdgger, 1906. An arfvedsonite-granite com- 
paratively poor in quartz, containing soda-micro- 
cline and microperthite, with arfvedsonite and 
aegirine. The rock is normally equigranular, but 
passes marginally into ekerite-porphyry. 

(Eker, Christiania district.) 

Elaterite. A variety of bitumen which, when fresh, is 
characterised by being elastic, but which, on expo- 
sure, becomes hard and brittle. 

Elaeolite-Syenite, Blum, 1861. A synonym for Nephe- 
line-syenite, now falling into disuse, except in so 
far as it is restricted to comparatively coarsely- 
grained types which contain the massive variety of 
nepheline distinguished, on account of its greasy 
lustre, as elseolite. 

Elasticity of Bulk. - - The property possessed by all 
substances whereby they tend to recover their ori- 
ginal volume after being compressed or extended. 

Elasticity Of Form (Rigidity). - - The property pos- 
sessed by solid bodies whereby they tend to recover 
their original form after being distorted. A per- 
fectly rigid body is one which cannot be deformed 
by any stress whatever. 

Electrostatic Separation. The separation of minerals 
according to their electrical conductivity, good con- 
ductors, such as ilmenite, being attracted by a 
charged body, while bad conductors such as 
quartz are unaffected. 
T. Crook : Min. Mag., xv, 1909, p. 260; xvi, 1911, p. 109. 

Ellipsoidal. A structural term applied to spilitic and 
similar rocks which, as a result of the conditions 
under which they consolidated, are disposed in a 
series of sack- or pillow-like masses. = Pilloiv 
J. V. Lewis : Butt. Geol. Soc. Am. y xxv, 1914, p. 595. 


Elutriation. The process whereby sand or other loose 
detritus is separated into grades by cur- 
rents of water of known and controlled velocity. 
Using upward-moving currents of water at 15 C. 
a velocity of 6.7 m.m. per second suffices to separ- 
ate silt from sand, and one of 0.12 m.m. per second, 
mud from silt. 

T. Crook : In Sedimentary Rocks (Hatch & Rastall), Lon- 
don, 1913, p. 349. 

P. G. H. Boswell : British Resources of Refractory Sands, 
London, 1918, p. 20. 

Eluvium. A general term, used more particularly by 
Continental and American writers, for residual 

Elvan. A Cornish name (el = rock ; van = white, 
Keltic) sometimes systematised as elvanite, for 
quartz-porphyry and other dyke rocks of similar 
composition. The term Blue Elvan is applied to 

Emery-rock. A granulose rock consisting essentially 
of corundum and iron-ores, which may be formed 
by magmatic segregation or by the metamorphism 
of laterite. The term emery, alone, connotes the 
commercial product obtained by crushing the rock. 

G. S. Rogers : Ann. New York Acad. Sci., xxi, 1911, p. 66. 

H. Miiller : Zeit. f. Prakt. Geol., xxiv, 1916, p. u. 

Enantiotropic. A term applied to the transition of 
one polymorphic form of a substance to another 
(e.g., quartz^=r>tridymite) when the change can 
take place in either direction according to the con- 

Enclaves, Lacroix, 1893. - - A general term for en- 
closures or inclusions of any kind contained in 
igneous rocks. The types recognised by Lacroix 
are set forth in the following four paragraphs. 

A. Lacroix : Les Enclaves des Roches volcamques, Paris, 
1893, p. 8 ; La Montagne Pelee et ses Eru-ptions, 1904, p. 


Enclaves Enallogenes. Xenoliths or accidental in- 

Enclaves HomoeOgeneS. Autoliths or cognate in- 
clusions- formed from the same magma as the 
enclosing rock. They are respectively described as 
(a) synmorphes (synmorphous), when they have the 
same textures as the enclosing rocks ; (b) plesio- 
morphes, when they have similar but not identical 
textures ; and (c) allomorphes, when the textures 
are notably different from those of the enclosing 
rocks. These types in turn may be homologues, 
when the composition of enclave and enclosing rock 
is the same, or antilogues, when the compositions 
are different, that of the enclave being always the 
more basic. 

Enclaves Pneumatogenes. -- Enclaves formed at 

great depths by the action of the volatile fluxes of 
the magma. 
A. Lacroix : Bull. Soc. franf. Min., xxiv, 1901, p. 488. 

Enclaves PolygeneS. Enclaves formed by the action 
of the magma or its volatile fluxes on another type 
of enclave. 

Enclosures. -- A term applied to allothigenous frag- 
ments of rocks or minerals included in igneous 
rocks ; generally referred to as inclusions. 
S. Powers : Journ. Geol., xxiii, 1915, pp. i and 166. 

Endogenetic. A term applied to geological processes 
originating within the earth, and to rocks, ore- 
deposits, and land-forms which owe their origin to 
such processes. Contrasted with Exogenetic. 
T. Crook : Min. Mag., xvii, 1914, p. 72. 

Endogenous Enclosures. = Cognate Inclusions. 

Endomorphism, Fournet, 1867. - The modification 
produced in an igneous rock due to the partial or 
complete absorption (assimilation) of portions of 
the rocks invaded by its magma ; a phase of con- 
tact-metamorphism in which attention is directed 
to the changes suffered by the intrusion instead of 
to those produced in the invaded formations. 


Enrichment. - - The sum of the secondary processes 
whereby one part of an ore-deposit is enriched at 
the expense of the parts above. 
W. H. Emmons : U.S.G.S. Bull., 625, 1917. 

Eo-, Nordenskiold, 1893. - - A prefix indicating the 
alteration of volcanic rocks bv devitrification or re- 
crystallisation ; e.g., Eorhylite, eoandesite, etc. 
Cf. Apo-. 
O. Nordenskiold : Bull. Gebl. Inst. U-psala^ i, 1893, p. 153. 

Eozoon. - - The generic name of a supposed foramini- 
feral fossil occurring in the Grenville Limestone ; 
now known to be an inorganic aggregate of pairs 
of minerals such as calcite and serpentine. 
H. J. Johnson-Lavis & J. W. Gregory: Sci. Trans. Roy. 
Dublin Soc., v, 1894, p. 259. 

Epi-, Giimbel, 1888. A prefix, indicating alteration, 
properly used as a qualifier to the names of rocks 
which have suffered a change in mineral composi- 
tion, but wrongly used in epidiorite, where it is 
added to the name of a rock (diorite) analogous in 
mineral composition to that of another rock 
(dolerite) as modified by alteration. The following 
terms are thus synonymous or nearly so- -epidiorite 
(Giimbel), epidiabase (Issel), epidolerite, and apodo- 
lerite (Van Rise). 

Epi-, Grubenmann, 1907. A prefix used as a qualifier 
to the group-names suggested by Grubenmann for 
metamorphic rocks, to indicate that the type so dis- 
tinguished belongs to the " upper zone " of meta- 
morphism. In this zone the distinctive physical 
conditions are moderate temperature, lower hydro- 
static pressure and powerful stress, and the rocks 
characteristically produced include mylonites, and 
cataclastic rocks generally, phyllites, chlorite- 
schists, talc-schists, porphyroids, and in part 
marbles and quartzites. Cf. Meso- and Kata-. 
U. Grubenmann : Die Kristallinen Schifer, II, 1907, pp. 
21, 172. 



EpiclastlC, Teall, 1887. -- A term applied to clastic 
rocks formed by exogenetic processes, i.e., to detri- 
tal sediments formed at the surface of the earth. 

Epidiabase, Issel, 1892. A term proposed in place of 
et>idiorite in order to avoid confusion with the term 
diorite. British writers, however, have continued 
to use the older term, denned below. 

Epidiorite. Gunibel, 1874. A doleritic or basaltic rock 
in which the augite has suffered alteration to horn- 
blende, so that the rock approaches the composi- 
tion of a diorite. Distinguished from cliabasc by 
the less extreme alteration of the felspars. 
J. S. Flett : Men?. GeoL Surv., 359 (Lizard), 1912, p. 102. 

Epidosite, Reichenbach, 1834. - - A term applied to 
altered igneous rocks, or veins traversing- them, 
essentially containing- epidote and quartz, and 
generally other secondary minerals such as uralite 
and chlorite. 

J. S. Flett : Mem. GeoL Surv. (Lizard), 1912, p. 50. 

F. L. Stillwell : Aust. Ant. Ex-p. Sci. Re-p. A, iii I (i) (Met. 
Rocks, Adelie Land), 1918, p. 58. 

Epigene. A. Geikie, 1879. A general term for geolo- 
gical processes originating at or near the surface 
of the earth. By Judd the term was later adopted 
as a group name for volcanic and sedimentary 
classes of rocks. Cf. Plypogene ; Exogenetic. 

Epigenetic. A term now generally applied to ore-de- 
posits of later origin than the rocks among which 
they occur ; contrasting them with those that are 
contemporaneous with the enclosing rocks (syn- 

Equigranular. A term applied to the texture of rocks 
whose essential minerals are all of one order of size. 

Equilibrium. - - The state of a system when all the 
operative forces so balance each other that the sys- 
tem would continue to remain in the same state 
indefinitely, provided no change were made in tem- 
perature, pressure, or composition. 


Erosion. The action of various mechanical agents in 
wearing- down the land ; generally restricted to pro- 
cesses acting by lateral rather than by vertical ex- 
cavation, those in which the latter action predomi- 
nates being- distinguished under the term 

Espichellite, Souza-Brandao, 1907- A mafic dyke- 
rock containing phenocrysts of olivine and 
hornblende with smaller ones of pyroxene, mag- 
netite and pyrite, in a groundmass composed of 
various mafic minerals, orthoclase-mantled labra- 
dorite, and alteration products such as calcite, 
chlorite, serpentine, and analcite. 

(C. Espichel, near Lisbon.) 

V. Souza - Brandao : Ann. Acad. Polytech. do Porto 
(Coimbra), 1907, ii, p. 30. 

Essential. A term applied to minerals whose presence 
in a rock helps to decide the choice of specific 
name given to the rock, and whose recognition is 
thus a necessary preliminary to the diagnosis of 
the rock. An essential constituent is not neces- 
sarily a major constituent, for the presence in a 
rock of quite small amounts of such minerals as 
nepheline, olivine, or quartz, may radically affect 
its classification ; these minerals are therefore 
always essential, unless merely local traces are 

Essexite, Sears, 1891. A phanerocrystalline igneous 
rock regarded as an alkali variety of gabbro, con- 
taining green and purple pyroxenes and plagio- 
clase (andesine to bytownite) with or without soda- 
amphiboles and olivine. Among the felsic minerals 
nepheline or analcite may occur in small amounts, 
and orthoclase or soda-orthoclase is always 
developed. By decrease in potash-felspar and 
increase of the felspathoid minerals the type passes 
into therdlite. (Essex Co., Mass.) 

A. Scott : Geol. Mag., 1915, pp. 455 and 513. 
A. Lacroix : C .R,, clxx, 1920, p. 20. 


Esterellite, Michel Levy, 1897. A holocrystalline 
variety of dacite or quartz-microdiorite, containing- 
phenocrysts of quartz, zoned andcsine, and horn- 
blende. (Esterel, France.) 
A. Michel Levy : Bull. Surv. Carte. Geol. France, ix. No. 
57, 1897, p. 19 

Ethmolith, Salomon, 1903. An injected transgressive 
igneous intrusion, having- the form of an irreg-ular 
funnel. The only example described is that of the 
Adamello tonalite. 

W. Salomon : Sitz K. -preuss. Akad. Wiss., -phys-math. 
Classe, xiv, 1903, p. 310. 

Elicrite, Rose, 1835. A variety of gabbro formed es- 
sentially of bytownite-anorthite and augite. The 
term has also been applied to meteorites of a simi- 
lar mineral composition. 

A. Harfcer : Mem. Geol. Surv. Scot.. 60 (Small Islejs), 1908. 
p. 97. 

Eugranitic Texture, Brogger. See Granitic. 
Euhedral, Pirsson, 1896. See Idiomorphic. 
Euktolite, Rosenbusch, 1899. See Venanzite. 

Eulysite, Erdmann, 1849. A granulose \-ariety of py- 
roxene-peridotite containing- mang-aniferous faya- 
lite and g-arnet and abundant magnetite. 

(Tunaberg-, Sweden.) 

]. Palmgren : Bull. Geol. Inst. U-psala, xiv, 1915, p. 109. 
Euphollte, Cordier, 1868. - - A variety of euphotide 
characterised by the presence of talc. 

Euphotide, Hatiy, 1822. A term orig-inallv svnony- 
mous with gabbro, and referring- to the reflection of 
lififht bv the green diallag-e present. The rock to 
which the name was first applied was afterwards 
found to have suffered saussuritisation, and con- 
sequently the term is now applied to g-abbros 
whose felspars have been altered in that way. 
T. G. Bonney : Phil. Mag., xxxiii, 1892, p. 237. 

Eurite, D'Aubuisson, 1819. A g-eneral term applied 
to compact felsitic rocks without phenocrysts, hav- 


ing the composition of quartz-porphyry or por- 
phyry. The term has also been used in an ex- 
tended sense to cover all aphanitic rocks of grani- 
tic composition whether porphyritic or not. 
G. A. J. Cole & A. V. Jennings : Q.J.G.S., xlv, 1889, p. 426. 

Eutaxic, Keyes, 1901. - - A general term applied to 
stratified ore-deposits, as opposed to those that 
are unstratified, or ataxic. 

C. R. Keyes : Trans. Amer. Inst. Min. Eng., xxx, 1901, p. 
3 2 3- 

Eutaxitic Structure. A term describing the streaked 
or blotched appearance of certain volcanic rocks 
due to the alternation of bands or elongated lenses 
of different colour, composition or texture ; the 
bands, etc., having been originally ejected as in- 
dividual portions of magma which were drawn out 
together in a viscous state and formed a hetero- 
geneous mass by welding. Cf. Flow-breccia. 

Eutectic Mixture. -- A discrete mixture (not a com- 
pound) of two or more minerals which have cry- 
stallised simultaneously from the mutual solution 
of their constituents, the two or more minerals 
being in definite proportions. Simultaneous cry- 
stallisation sometimes gives rise to graphic texture, 
but it does not necessarily do so, as the develop- 
ment of graphic intergrowth involves other factors 
besides eutectic proportions. 
A. L. Day : Bull. Geol. Soc. Am., xxi, 1910, p. 147. 

Eutectic Point. The lowest temperature, at any given 
pressure, at which the constituents of two (or 
more) minerals can exist together in a liquid state 
of mutual solution, and at which the two (or more) 
minerals can crystallise simultaneously in a 
constant proportion to each other by weight. 

Eutectic Ratio. The ratio by weight of two minerals 
which crystallise at the eutectic point simultan- 
eously from the mutual solution of their consti- 


Evergreenite, Ritter, 1908. A variety of nordmarkite 
characterised by the presence of sulphide-ores (chal- 
copyrite and bornite). 

(Evergreen Mine, Colorado.) 

E. A. Ritter : Trans. Am. Inst. Min. Eng., xxxviii, 1908, 
p. 751; U.S.G.S. Prof. Paf., 94, 1917, p. 127. 

Exogenetic. A term applied to geological processes 
originating at or near the surface of the earth (e.g., 
denudation and deposition), and to rocks, ore-de- 
posits, and land forms which owe their origin to 
such processes ; contrasted with Endogenetic. 
T. Crook : Min. Mag., xvii, 1914, p. 72. 

Exogenous Enclosures. = Accidental inclusions, = 
xenoliths and xenocrysts. See Enclaves. 

Exomorphism, Fournet, 1867. The modification pro- 
duced in the invaded rocks by intrusions which 
traverse them ; = Contact metamorphism in the 
usual sense, as opposed to endomorphism. 

Explosion-tuffs, Green, 1919. Tuffs of which the con- 
stituents have been dropped directly into place after 
being ejected from a volcanic vent, the term thus 
distinguishing such tuffs from the more ordinary 
types which are washed into place. 
J. F. N. Green : Proc. Geol. Assoc., xxx, 1919, p. 155. 

Fabric, C.I.P.W., 1902. A term suggested for that 
part of a texture which depends on the shapes and 
arrangement of the constituents of a rock ; texture 
being considered as a function of crysLallinity, 
granularity, and fabric. 

Facies. A term denoting " the sum of the lithological 
and palseontological characters exhibited by a 
deposit " regarded as criteria of the conditions 
which controlled their formation (e.g., alluvial, 
glacial, littoral facies, etc.). Also applied to 
varieties of a single body of igneous rock which 


differ in structure or composition from the normal 

rock-type of the mass. 
Fahlbaild. -- A Scandinavian mining- term for meta- 

morphic rocks heavily impregnated with iron-ores 

or sulphide minerals. 
Fakes. A vernacular term for platy formations such 

as micaceous flagstones associated with oil-shales 

or coal-seams. 

False-cleavage, Marker, 1885. -- See Strain-slip- 

A. Harker : Rep. Brit. Assoc. (1885), 1886, p. 836. 
Fanglomerate, Laws on f 1913. A term proposed for 
the coarser deposits occurring in the upper parts 
of alluvial fans. 
A. C. Lawson : Bull. Dept. Geol. Univ. California, vii, No. 

1 5> I 9 1 3> P- 3 2 9- 

Farrisite, Brogger, 1898. -- An aphanitic dyke rock 
containing barkevikite and diopside as its chief 
mafic minerals, with lepidomelane, olivine and 
magnetite in smaller quantities, the felsic minerals 
felspar and nepheline, being almost entirely altered 
to, or replaced by zeolites. 

(Farris See, Christiania District.) 
W. C. Brogger : Eruptivgest. Kristiania, iii, 1898, p. 64. 

Fasibitikite, Lacroix, 1915. A mesocratic variety of 
riebeckite-cegirine-gpranite containing eucolite and 
zircon. (Ampasibitika, Madagascar.) 

A. Lacroix : C.R., clxi, 1915, p. 253. 

A Holmes : Geol. Mag., 1915, p. 267. 

Fasinite, Lacroix, 1916. A phanerocrystalline rock 
composed essentially of augite and nepheline, with 
subsidiary olivine, biotite, etc. The type is 
chemically equivalent to berondrite, and differs 
from bekinkinite by the absence of hornblende and 
A. Lacroix: C.R., clxiii, 1916, p. 257; clxx, 1920, p. 20. 

Felsic, C.I.P.W., 1912. A mnemonic term (recalling 
felspar, /eZspathoid and silica) for felspathic mine- 
rals and quartz actually present in an igneous 


rock, and also for rocks largely composed of such 
minerals; not synonymous with salic which refers 
to the normative compounds of a rock calculated 
from its analysis. 
C.I.P.W. : Journ. Geol., xx, 1912, p. 561. 

Felsite. An igneous rock with or* without phenocrysts, 
in which either the whole or the groundmass con- 
sists of cryptocrystalline aggregates of felsic 
minerals, quartz and orthoclase being those char- 
acteristically developed. When phenocrysts of 
quartz are present the rock is termed Quartz-fel- 
site or Quartz-porphyry, the latter term being now 
more customary than the former. 

Felsitic. A term applied to the cryptocrystalline tex- 
ture seen in the groundmass of quartz-felsites and 
similar rocks ; and which may be original as the 
result of a rapid cooling of a viscous magma, or 
secondary, as the result of the devitrification of a 
natural glass. By many authors this texture is 
described as micro/ els itic, the term felsitic alone re- 
ferring only to the aphanitic appearance of a hand 
specimen. The latter, examined in thin section, 
may then be micro granitic, micro graphic, ortho- 
phyric, micropoikilitic, or microfelsitic, etc. 

Felsophyre, Vogelsang, 1867. -- A general term for 
porphyries and quartz-porphyries having a felsitic 
or cryptocrystalline groundmass. 

Felspathic-tawite. A phanerocrystalline rock, inter- 
mediate in composition between taivite and soda- 
lite-syenite composed essentially of sodalite and 
alkali-felspar (the former being predominant) with 

J. J. O'Neill : Geol. Surv. Canada Mem., 43 (Pub. Xo. 
1,311), 1914, p. 46. 

Femic, C.I.P.W., 1902. A mnemonic term (recalling 
/errowagnesian) for the group of standard norma- 
tive minerals, in which the pyroxene and olivine 
molecules and most of those of the accessory 
minerals appear. The corresponding term for the 


ferromagnesian minerals actually present in a rock 
is mafic. 

FergUSite. A variety of shonkinite or melanocratic 
nepheline-syenite, containing- orthoclase-nepheline 
pseudomorphs after leucite. 

(Fergus Co., Montana.) 
L. V. Pirsson : U.S.G.S., Bull. 237, 1905, p. 83. 

Ferricrete, Lamplugh, 1902. A term suggested for 
conglomerates formed by the cementation of 
gravels by the oxidation of percolating solutions 
of iron salts. 
G. W. Lamplugh : Geol. Mag., 1902, p. 575. 

Ferrite, Vogelsang, 1872. A general non-committal 
descriptive term for reddish-brown amorphous 
alteration products which are presumably ferru- 
ginous, but which cannot be definitely diagnosed by 
ordinary optical methods. 

Ferrolite, Wads-worth, 1891. -- A general term pro- 
posed for iron-ore rocks. 

Fireclay. A general term for refractory clays which 
resist exposure to high temperatures without dis- 
integrating or becoming soft and pasty by melting. 
Such clays are abundant beneath the coal seams 
of the Coal Measures, and are characterised 
chemically by a low content of alkalies and lime. 
W. M. Hutchings : Geol. Mag., 1891, p. 164. 
J. W. Gregory : Proc. Roy. Soc. Edin., xxx, 191, p. 348. 
A. H. Cox : Geol. Mag., 1918, p. 56. 

Flaser-gabbro. - - A term for dynamically meta- 
morphosed gabbro which has been crushed and 
sheared into lenticular masses separated by wavy 
ribbons and streaks of finely granulated and recry- 

(stallised material. The phacoidal relics of the 
original rock have not lost their igneous character, 
and the rock as a whole has not become a schist. 
J. S. Flett : Mem. Geol. Surv., 359 (Lfzard), 1912, p. 87. 

neiss. A general term for dynamically meta- 
morphosegj rocks, usually igneous, which, like the 
flaser-gabbro defined above, still contain coarse- 


grained lenticular masses or phacoids of parts of 
the original rock in a finely crystalline foliated 

Fleckschiefer. See Spotted Slates. 

Flint. A more or less pure siliceous rock composed 
mainly of granular chalcedony together with a 
small proportion of opaline silica, and occurring 
in nodules, irregular concretions, layers, and vein- 
like masses in the Chalk. The fracture is conchoi- 
dal, whereas in chert a splintery fracture is more 

W. Hill : Proc. Geol. Assoc., xxii, 1911, p. 61. 

G. A. J. Cole : Geol. Mag., 1917, p. 64. 

W. A. Richardson : Geol. Mag., 1919, p. 535. 

Flinty Crush-rock, Clough. A black flinty product of 
dynamic metamorphism associated with mylonite, 
and representing a fritted or partly fused variety of 
the latter ; generally structureless, but occasionally 
showing incipient traces of crystallisation. 

Mem. Geol. Surv. (N.W. Highlands), 1907, pp. 124, 221, 249. 

S. J. Shand : Q.J.G.S., Ixxii, 1916, p. 209. 

Flowage. A term, applied to the deformation of rocks, 
stressed beyond the limit of elastic recovery, by 
plasticity (molecular flow), granulation (closely- 
spaced fracturing), gliding (on cleavage planes), 
or recrystallisation. 
J. Barrell : Journ. Geol., xxiii, 1915, p. 427. 

Flow-breccia. - - A term describing lavas in which 
fragments of partly solidified magma, produced by 
explosion or flowage, have become welded together 
or cemented by the still fluid parts of the same 

Flow Structure. A structure, generally, but not ne- 
cessarily, restricted to volcanic rocks, in which the 
stream lines of the magma are revealed by alter- 
nating bands of differing composition, crystallinity 
or texture, or by a sub-parallel arrangement of 
prismatic or tabular crystals. 


Fluxion Gneiss, Gregory, 1894. A gneis&ose or band- 
ed igneous rock with a fluxion structure due to the 
movements of a viscous magma during the later 
stages of crystallisation. Cf. Primary foliation. 

Fluxion Structure. A structure of igneous rocks due 
to the movement involved in intrusion or to con- 
vection, and evidenced by the parallel or sub-paral- 
lel disposition of adjacent phenocrysts, or by the 
alternation of mineralogically unlike layers. The 
latter type of structure is generally distinguished 
as banded. 
F. F. Grout : fourn. Geol., xxvi, 1918, p. 439. 

Foliation, Darwin, 1846. A structure represented 
most characteristically in schists, due to the 
parallel disposition in layers or lines of one or more 
of the conspicuous minerals of the rock, the 
parallelism not being a direct consequence of 
stratification. The layers may be plane lamellae, 
gently undulating or strongly crumpled, or they 
may be lenticular or phacoidal. Foliation may be 
described as closed when the minerals to which the 
structure is due form a megascopically felted aggre- 
gate, and as open when the controlling minerals are 
megascopically discontinuous or in disconnected 
T. G. Bonney : Geol. Mag., 1919, p. 196. 

Foliate, Bastin, 1909. A general term for any foliated 

Forellenstein, ^. Rath. = Oss y pite = Troctolite. 

Formation. A term applied stratigraphically to a set 
of strata possessing a- common suite of lithological 
and /or faunal characteristics. 

Fortunite, de Yarza, 1896. A variety of verite com- 
posed of phenocrysts of olivine and phlogopite in 
a brown glass containing small crystals of py- 
roxenes, biotite and orthoclase. (Fortuna, Spain.) 
A. Osann : Festschrift H. Rosenbusch, Stuttgart, 1906, p. 


Fourchite, Williams, 1890. An olivine-free monchi- 
quite characterised by an abundance of titanaugite. 

(Fourch Mts., Montana.) 

J. F. Williams : Geol. Surv. Arkansas Ann. Rep., ii, 1890, 
P- 107. 

Foyaite, Blum, 1861. A nepheline-syenite consisting 
of perthitic-orthoclase, microline, and nephe- 
line, with soda-pyroxenes and/or amphiboles. By 
Roseribusch the term is applied to all varieties of 
nepheline-syenite which contain dominantly potash 
felspars, and this is the common usage of the 
term. Brdgger, however, has caused a certain 
confusion in its use by giving the term a textural 
significance, all nepheline-syenites with a trachy- 
toid texture being joyaite according to his defini- 
tion. (Foya, Serra de Monchique, Portugal.) 

Fruchtschiefer. See Spotted Slates. 

Fulgurite, Arago f 1821. A glassy and often tube-like 
mass produced by the action of lightning on loose 
or compact rocks. 
A. A. Julian : Journ. Geol., ix, 1901, p. 673. 

Fuller's Earth. A very fine-grained deposit consisting 
chemically mainly of hydrated aluminium silicate, 
but differing from ordinary clay in its unusually 
low plasticity. It is used for degreasing wool and 
for clarifying oil. (Cotteswolds, and Surrey.) 

C. L. Parsons : V .S. Bureau of Mines, Bull. 71, 1913, p. 6. 

G. M. Davies : Proc. and Trans. Cray don Nat. Hist, and 
Sci. Soc., 1915-16, pp. 63, 92. 

Fusain, Stevenson, 1911. A term suggested to replace 
" mother of coal " and " mineral charcoal " ; i.e., 
for an ingredient of bituminous coal which con- 
sists of fibrous strands forming patches and wedges 
somewhat flattened parallel to the bedding plane. 
In thin section fusain appears black and nearly 
opaque, but may show the cellular structure of 

Marie C. Stopes : Proc. Roy. Soc. B., xc, 1919, pp. 472-4, 


Fusion Point. The temperature at which a crystalline 
substance undergoes a discontinuous change from 
the solid to the liquid state, absorbing latent heat 
while the change is effected. The term has no 
precise meaning as applied to materials such as 
glass, or rocks composed of more than one mineral. 
= Melting-point. 

A. Plarker : Nat. Hist. Ig. Rocks, 1909, p. 153. 
A. L. Day : Fort, der Min. Krist. Pet., iv, 1914, p. 189. 


Gabbro, von Buck, 1810. A phanerocrystalline rock 
consisting of labradorite, or bytownite, and augite 
(generally diallage). With the incoming of olivine 
the rock becomes Olivine- gabbro. If the plagio- 
clase be anorthite, the term Eucrite may be used. 

W. S. Bayley : Journ. Geol., i, 1893, p. 433. 

J. W. Sollas : Trans. Roy. Irish A cad., xxx, 1894, p. 477 

A. Harker : Q.J.G.S., 1, 1894, p. 311 (Carrock Fell). 

Mem. Geol. Surv. (Tert. Ig. Rocks, Skye), 1904, p. 102, 

Mem. Geol. Surv. Scot., 60 (Small Isles), 1908, p. 93. 
J. S. Flett : Mem. Geol. Surv., 359 (Lizard), 1912, p. 81. 
M. N. Nebel : Econ. Geol., xiv, 1919, p. 367 (Duluth). 

H. C. Cooke : Geol. S:trv. Canada Mus. Bull. 30, 1919 

Gabbro-Syenite, Tarassenko, 1895. A descriptive 
name for rocks now known as monzonite, in which 
the plagioclase is at least as calcic as labradorite. 
= Orthoclase-gabbro. Cf. Granogabbro 

Gallaston Basalt, Hatch, 1892. A type of the Scottish 
Carboniferous basalts, intermediate between the 
Jedburgh and Dalmeny types ; characterised by 
abundant small phenocrysts of olivine relative to 
those of plagioclase, in an ophitic groundmass. 
F. H. Hatch : Q.J.G.S., xlviii. 1892, p. 129. 

Gangue. -- A general term for the non-metalliferous 
mineral aggregates associated with ores in mineral 


Canister. A compact, highly siliceous sedimentary 
rock, with a fine and even granular texture ; com- 
posed of medium to fine grains of angular quartz 
cemented with silica. 

Mem. Geol. Surv. S-pec. Rep. Mineral Resources of Great Bri- 
tain, vi, 1918, p. 3. 

Garbenschiefer. See Spotted Slates. 

Garwaite, Duparc cV Pearce, 1904. -- A variety of 
peridotite-porphyrv containing phenocrysts of 
diopside in a micro-granular groundmass com- 
posed of pyroxene, olivine, magnetite, and 
chromite. (Tilai Range, N. Urals.) 

L. Duparc & F. Pearoe : C.R., cxxxix, 1904, p. 154. 

Garganite. Viola &> de Stefani, 1893. A variety of 
vogesite containing both augite and hornblende. 

Gauteite, Hibsch, 1897. A variety of rrachyandesite 
occurring as dykes ; a bostonite-like rock with 
micro-phenocrysts of andesine. (Gaute, Bohemia.) 

Gebtirite-dacite, Gregory, 1901. -- A holocrystalline 
variety of dacite occurring as a dyke rock, and 
characterised by the presence of hypersthene. 
J. W. Gregory : Proc. Roy. Soc. Victoria, xiv, 1902, p. 193. 

Gel. A colloidal aggregate composed of two phases, 
as in a jelly ; one phase forming a continuous 
framework enclosing cells occupied by another 
(liquid) phase. 

Generation. A term applied to each of two or more 
groups of crystals of the same mineral in igneous 
rocks, when the sizes of the crvstals in the different 
groups are conspicuously different. Thus, if pheno- 
crysts of orthoclase are embedded in a groundmass/ 
containing crystals of orthoclase, the former are 
said to belong to an earlier generation than the 
latter, and the two groups are considered to in- 
dicate different periods of formation corresponding 
to changes in the cooling conditions. 

Geode. A hollow secretion or concretion, lined with 
crystals on the inside walls, and separable as a 


discrete nodule from the rock (usually argillaceous 
or calcareous) in which it occurs. Cf. Druse. 

R. S. Bassler : Proc. U.S. Nat. Museum, xxxv, iqo8, p. 133. 
F. M. Van Tuyl : Am. Jo^^rn. Sci. } xlii, igi6, p. 34. 

Geological Thermometer. A term applied to known 

temperature limits within which certain minerals 
or mineral aggregates must have formed ; based 
on the thermal data relating to the fusion-points of 
rocks and minerals, and the inversion- or transi- 
tion-points of allotropic modifications of rock- 
forming- compounds, and in general to the equili- 
brium conditions and stability ranges under dif- 
ferent conditions of pressure for various minerals, 
allotropes, solid-solutions, eutectics, and other 
mineral ag-gregates. 

F. E. Wright & E. P. Larsen : Am. Journ. Sci., xxvii, 1909, 
p. 421. 

A. L. Day : Bull. Geol. Soc. Am., xxi, 1910, p. 176. 

Geyserite. A general term for the siliceous deposits, 
usually opaline, formed around thermal springs 
and geysers, whether loose, compact, or con- 

Ghizite, Washington, 1914. A variety of analcite- 
basalt characterised by the presence of biotite. 

(Mt. Ferru, Sardinia.) 
H. S. Washington : Journ. Geol., xxii, 1914, p. 748. 

Gibelite, Washington, 1913. A variety of alkali- 
trachyte, containing- soda-microcline, with small 
amounts of colourless to green augite and dark- 
brown hornblende. (Pantelleria.) 

H. S. Washington : Journ. Geol., xxi, 1913, p. 684-91. 

Gieseckite-porphyry. An altered nepheline-porphyry 
in which porphyritic crystals of nepheline are re- 
placed by s.caly sericitic aggregates. =Liebenerite- 
porphyry. (Greenland.) 

Gilsonite. See Uintaite. 

Giumarrite, Viola, 1901. -- A variety of amphibole- 
monchiquite. (Giumarra, Sicily.) 


Gladkaite, Duparc &> Pearce, 1905. A quartz-lam- 
prophyre containing- andesine and hornblende, 
and in smaller quantities both micas and epidote = 
quartz spessartite. (Gladkaia Sopka, N. Urals.) 
L. Duparc & F. Pearce : Mem. Soc. de Phys. e t tfHist. 
Nat. Geneva, xxxviii, 2, 1914, p. 136. 

Glass. A general term for the amorphous consolida- 
tion products of mag-mas, whether forming- the 
whole of a rock, as in obsidian or pumice, or only 
a groundmass or mesostasis. Glass natural or 
artificial is described physically as a rigid solution 
to distinguish it from solid solutions which are 
necessarily crystalline. 

N. L. Bowen : Journ. Wash. Acad. Sci, viii, jqi8, p. 88. 

G. V. Wilson : Journ. Soc. Glass Tech., ii, 1918, p. 177. 

GlailCOphane-SChist, Barrois, 1883. A well-marked 
type of amphibole-schist, in which glaucophane in- 
stead of hornblende is an abundant mineral. 
Epidote is frequently present, and quartz and mica 
varieties are recognised. 

H. S. Washington : Am. Journ. Sci., xi, IQOI, p. 35. 

E. Murgoci : Bull. De-pt. GeoL Univ. California, iv, 1906, 

P- 359- 

Globigerina Ooze, Ehrenberg^ cV Bailey, 1853. A 
widespread deep-sea deposit largely composed of 
the shells of foraminifera, among which Globigerina 
is especially abundant. Other calcareous remains 
are present (about 10 per cent.), together with an 
inorganic residue (about 3 or 4 per cent.) having 
the composition of red clay (q-v.). 

J. Murray & A. F. Renard : " Challenger " Re-h. (Deep Sea 
Deposits), 1891, p. 213. 

Globosphaerite, Vogelsang, 1872. See Globulite 


Globulite, Vogelsang, 1872. - - An extremely minute 
sphere-like crystallite, i.e., having no reaction on 
polarised light. When loosely aggregated into 
irregular cloudy masses, the latter are known as 
ciimulites, while more closely aggregated masses 


are called globosph&rites. Linear strings of 
globulites are known as margantes. 
F. Rutley : Min. Mag., ix, 1891, p. 261. 

Glomeroplasmatic, Lcewinson-Lessing, 1900. A term 
applied to the texture of granites or gneissose rocks 
in which the individuals of a certain mineral (such 
as biotite) are locally concentrated into conspicuous 
open clusters, and not into closed groups as in 
glomeroporphyritic texture. 
A. Holmes : Q.J.G.S., Ixxiv, 1918, p. 55. 

Gfomeroporphyritic, ]udd, 1886. A texture produced 
by the; segregation of numerous crystals of the 
same mineral into compact and conspicuous groups 
which give the rock a porphyritic aspect. 

J. W. Judd : Q.J.G.S., xlii, 1886, p. 71. 
Gneiss. A foliated or banded phanerocrystalline rock 
(generally, but not necessarily, felspathic and of 
granitic or dioritic composition) in which granular 
minerals, or lenticles and bands in which they pre- 
dominate, alternate with schistose minerals, or 
lenticles and bands in which they predominate. 
The foliation of gneiss is more " open," irregular, 
or discontinuous than that of schist (q-v.). 

J. J. Sederholm : Bull. Comm. Geol. FinLande, No. 23, 
1907, p. 91. 

A. G. Hogbom : Bull. Geol. Inst. U-psala, x, 1910, p. 29. 

J. D. Trueman : Journ. Geol., xx, 1912, p. 236. 

J. S. Flett : Mem. Geol. Surv. (Lizard), 1912, pp. 55 and 119. 

J. J. H. Teall : Mem. Geol. Surv. (i\.W. Highlands), 1907, 
chap. v. 

A. Holmes : Q.J.G.S., Ixxiv, 1917, p. 52. 

Gneissose Granite. A general term for granitic rocks 

twith gneissose structure due, not to meta- 
morphism, but to the constrained movements of a 
viscous magma during crystallisation = Granite- 
gneiss = Primary igneous gneiss. 
G. Barrow : Q.J.G.S., xlix, 1893, p. 330. 
Gneissose Structure. - - The structure of phanero- 
crystalline rocks, having an open foliation, and in- 
termediate in character between schistose rocks 
with a closed foliation and granulose rocks 



with no foliation. Lamellar or prismatic minerals 
may be distributed in parallel planes or lines 
through the more granular body of the rock, or 
bands and lenticles of granular minerals may alter- 
nate with folise of lamellar minerals. 
Gondite, Fermor, 1909. -- A spessartite-quartz rock, 
probably produced by the metamorphism of man- 
ganiferous sediments, and named after the Gonds 
of the Central Provinces of India, where the 
Gondite Series occurs. 

L. L. Fermor : Mem. Geol. Surv. India, xxxvii, 1909, p. 306. 
Gondite Series, Fermor, 1909. - - A series of man- 
ganiferous rnetamorphic rocks belonging to the 
Dharwar System of India, and characterised by 
the presence of spessartite, rhodonite, and quartz. 
Gossan. A term applied to the weathered or other- 
wise decomposed upper zone of a lode, char- 
acterised by an abundance of oxidised and 
hydrated alteration products such as limonite. 
Grade. A term applied to those grains of any detrital 
sediment which are of the same order of size, the 
latter being conventionally determined by a range 
of diameters. In the mechanical analysis of 
sands, etc., the relative proportion of each grade 
is determined. The following classification of 
grade-sizes is used for this purpose : 
Name / Grade . Range of Diameters . 

Pebbles ... ... ... ... ... Greater thanio mm. 

Gravel ... ... 10 mm. _ 2 mm. 

very coarse sand... ... ... 2 mm. - i mm. 

coarse sand i mm. - 0.5 mm. 

medium sand 0.5 mm. -0.25 mm. 

fine sand 0.25 mm. - o.i mm. 

( superfine sand } o.i mm. -0.05 mm. 

o.,, I coarse silt J 

( silt ... ... ... ... 0.05 mm.~o.oi mm. 

Mud or clay ... ... ... ... Less than o.oi mm 

S. Oden : Proc. Roy. Soc. Edin., xxxvi, 1915-16, p. 219. 

P. G. H. Bos well : British Resources of Sands and Rocks 

used in Glass Making, and Ed., 1918, p. 13. 
A. Holmes : The Physical and Geological Characters of 
Concrete Aggregates, B.F.P.C. " Red Book," 256, 1920. 


Graded Sediments. - - A general term for loose or 
cemented detrital sediments in which the allogenic 
grains lie mainly within the limits of a single 

P. G. H. Boswell : Sands and Rocks used in Glass Making, 

Grahamite. (1) A type of meteorite belonging to the 

Me so side rite group ; (2) a variety of asphalt or 

asphaltite having a specific gravity of 1.15, and 

soluble in carbon disulphide. 

G. H. Eldridge : U.S.G.S., 22nd Ann. Re$., Pt. i, 1901, 

p. 221. 

Granite. A phanerocrystalline rock, consisting 
essentially 01 quartz and alkali-felspars with any 
of the following : biotite, muscovite, and amphi- 
boles and pyroxenes (including soda varieties in 
the alkali- granites). By increase of oligoclase or 
andesine relative to> the alkali-felspars, granite 
passes through adamellite (quartz-monzonite) to 
granodiorite and quartz-diorite (tonalite). By 
decrease of quartz, granite passes through quartz- 
syenite into syenite. 

A. Marker & J. E. Marr : Q./.G.S., xlvii, 1891, p. 266 (Shap). 

W. J. Sollas : Trans. Roy. Irish Acad., xxix, 1891, p. 427 

J. J. H. Teall : Mem. Geol. Surv. (Silurian Rocks, Scotland), 
1899, p. 607. 

P. J. Holmquist : Bull. Geol. Inst. U-psala, vii, 1906, p. 77 

Mem. Geol. Surv., 351, 352 (Land's End), 1907, p. 40. 

Mem. Geol. Surv., 347 (Bodmin and St. Austell), 1909, p. 54. 

R. H. Rastall : Q.J.G.S., Ixvi, 1910, p. 116 (Skiddaw). 

Mem. Geol. Surv., 338 (Dartmoor), 1912, pp. 27 and 37. 

Mem. Geol. Surv. Scot., 53 (Glen (Joe), 1916, pp. 119 and 135. 

P. Geijer : Bull. Geol. Inst. U$sala, xv, 1916, p. 47 (Sweden, 
Mechanics of Intrusion). 

R. H. Rastall & W. H. Wilcockson : Q.J.G.S., Ixxi, 1917, 
p. 592 (Lake District). 

Granite-porphyry. A rock differing from quartz- 
porphyry by its relative abundance of phenocrysts 
of granitic minerals, and by a generally coarser 
groundmass ; = porphyritic micro granite , which 


passes into porphyritic granite as the groundmass 
becomes phanerocrystalline. 

Granitic = Granitoid. - - Terms applied to irregularly 
granular textures like that of a non-porphyritic 
granite -y Eu granitic = Allotrionwrphic- granular. 

Granltite. Originally used to connote granitic rocks 
rich in oligoclase, the term is now applied to 
biotite-granite as denned by Rosenbusch. 

Granodiorite, Becker. A rock intermediate in com- 
position between quartz-diorite and quartz-mon- 
zonite, and in which the ratio of orthoclase to 
plagioclase falls between a third and a seventh. 
The term, however, is rarely used in this strict 
sense, and is more usually applied to rocks inter- 
mediate between quartz-diorite and granite. 

Granodolerite, Shand, 1917. A term suggested for 
oversaturated dolerites containing quartz and 
orthoclase, these minerals being generally pre- 
sent, but not necessarily, as interstitial micro- 

Granogabbro, ]okannsen, 1917. -- A term suggested 
for quartz-orthoclase-gabbros, i.e., for phanero- 
crystalline igneous rocks intermediate between 
quartz-labradorite-monzonite and quartz-gabbro. 

Granoiite, Pirsson, 1899. A general term suggested 
for phanerocrystalline igneous rocks having a 
granitic as opposed to a porphyritic texture ; 
Plutonic rock (in part). 

L. V. Pirsson : Journ. Geol., vii, 1899, p. 141. 
W. H. Turner : Journ. GeoL, viii, 1900, p. 105. 

Granophyre, Rosenbusch, 1872. - - A fine-grained 
granitic rock having a micrographic texture, or a 
granite- or quartz-porphyry having a micro- 
graphic groundmass. In an earlier usage of the 
term (Vogelsang, 1867) it connoted a porphyritic 
rock having a granitic composition, with a micro- 
granular groundmass. Cf. Graphophyre. Grano- 
phyres are frequently associated with gabbros and 
corresponding 1 to this and to their comparatively 


shallow origin, their chief mafic constituent is fre- 
quently augite ; biotite-bearing varieties, however, 
are not uncommon. 

A. Harker : Q.J.G.S., li, 1895, p. 125 (Carrock Fell). 

T. H. Holland : Q.J.G.S., liii, 1897, p. 416. 

Mem. Geol. Sur-v. (Tert. Ig. Rocks, Skye), 1904, p. 153. 

R. H. Rastall : Q.J.G.S., Ixii, 1906, p. 253 (EnnerdaleV 

A. R. Dwerryhouse : Q.J.G.S., Ixv, 1909, p. 55 (Eskdale). 

Granophyric. See Micrographic. 

Granularity. One of the features involved in the con- 
ception of texture ; the effect due to the magnitudes 
of the constituent crystals ; described by terms 
such as phanerocrystalline, microcrystaUine, etc. 
A. L. Queneau : School of Mines Quarterly, xxiii, 1902, p. 

Granular Texture. A texture due to the aggregation 
of mineral grains of approximately equal size, 
whether in clastic, igneous, or recrystallised rocks. 

W. Cross : U.S.G.S., iqth Ann. Re<p. (1892-3), p. 232. 

Granulation. The fragmentation of minerals strained 
beyond their elastic limit. The amount of granula- 
tion depends not only on the nature of the stresses, 
but also on the minerals themselves and their sizes 
and shapes. 

C. R. Van Hise : U.S.G.S. Mon., xlvii (Metamorphism), 
1904, pp. 673 and 737. 

Granulite, Weiss. A granulose metamorphic rock 
composed of even-sized interlocking granular 
minerals (e.g. , felspars, pyroxenes, and garnet). 
Parallel or banded structure is due either to the pre- 
sence of streaks and lenticles of non-granular 
quartz, or to the alternation of bands in which dif- 
ferent minerals predominate ; =Leptynite. The 
term granulite has been applied to muscovite- 
granites by Michel-LeVy. 
Mem. Geol. Surv. (N.W. Highlands), 1907, p. 64. 

Granulitic Structure. A structure due to the produc- 
tion of granular fragments in a rock by crushing. 
In France the same term has also been used as 
synonymous with panidionwrphic- granitic texture. 


Granulitic Texture, Judd, 1886. A doleritic or 

basaltic texture due to the arrangement of granular 
crystals of augite or olivine between a network of 
felspar laths. Cf. Inter granular. 
J. W. Judd: Q.J.G.S., xlii, 1886, p. 68. 

Granulose Structure. A structure characteristically 

developed in granulites, due to the presence of 
granular minerals, such as quartz, felspars, gar- 
nets and pyroxenes, in alternating streaks and 
bands developed on a megascopic or microscopic 
scale. Successive layers may differ in colour, tex- 
ture, or mineral composition, but typical foliation 
is absent on account of the absence of lamellar or 
prismatic minerals. 

Graphic Granite. A phanerocrystalline quartz-alkali- 
felspar rock, in which large crystals of the two 
minerals are intergrown in such a way that in sec- 
tion the intercalates of quartz have the appearance 
of cuneiform or Semitic characters. 
E. S. Bastin : Journ. Geol., xviii, 1910, p. 313. 
A. Holmes : Q.J.G.S., Ixxiv, 1918, p. 77. 

Graphic Texture. The cuneiform appearance seen in 
section, due to the interpenetration of quartz and 
felspar on a megascopic scale. Similar textures, 
though generally less regular, are sometimes 
developed between certain other pairs of minerals, 
the conditions necessary for the development of 
graphic and allied textures including the simul- 
taneous crystallisation of the minerals concerned 
from their eutectic. It does not follow, however, 
that graphic texture is a necessary consequence of 
eutectic crystallisation. 

Graphophyre, C.I.P.W., 1903. A term suggested in 
place of granophyre (Rosenbusch). The latter 
term was used by Vogelsang for porphyritic micro- 
granitic rocks, but as this usage has not been 
generally adopted, and the term granophyre is now 
universally used in its Rosenbusch sense, no con- 
fusion is caused by its retention. The terms 


graphophyre and graph ophyric have not yet been 
justified by usage, even though their derivation is 
more accurately descriptive. 

Gravel.- A loose detrital sediment in which the pre- 
dominant grade-size is from 2 to 10 mm. A 
deposit of more coarsely graded detritus is 
described as a pebble-bed, or a boulder-bed. Both 
stratigraphically and commercially, however, the 
term gravel is used to cover a wider range of 
grade-sizes than that defined above. 

Graywacke. A term applied to felspathic or tufface- 
ous grits and coarse sandstones, usually dark in 
colour, which are strongly cemented, often with an 
argillaceous binding, and occur characteristically 
among the older formations = Grau i wacke. 

Greenalite Rock. A dull dark-green rock of uniform 
fine grain and conchoidal fracture, containing 
grains of greenalite in a matrix of chert, car- 
bonate-minerals, and ferruginous amphiboles. 
C. R. Van Hise & C. K. Leith : U.S.G.S., Mon. Hi, 1911, 
pp. 165, 474. 

Green Mud. A deep sea terrigenous deposit, char- 
acterised by a considerable proportion of glau- 
conite ; CaCO 3 present in variable amounts up to 
50 per cent. 

J. Murray & A. F. Renard : " Challenger " Re-p. (Deep Sea 
Deposits), 1891, p. 236. 

Greensand. A general term for sandstones which, 
when un weathered, have a greenish hue due to the 
presence of kernels and grains of glauconite. 

Green Schist. A general term for those varieties of 
schists in which hornblende, chlorite, or epidote are 
abundant constituents. 

Greenstone. An old field-term applied to more or less 
altered basaltic or doleritic rocks, the characteris- 
tic dark green colour being due to the presence of 
chlorite, hornblende, epidote, etc., as in diabase 
and epidiorite. 

G. H. Williams : U.S.G.S. Bull., 62, 1890. 
J. S. Flett : Mem. Geol. Surv. (Land's End), 1907, p. 31. 


Werner. - - A primary or pneumatolytirally- 
altered rock of granitic or aplitic texture, contain- 
ing- quartz, and alkali-micas, and generally, though 
not necessarily, topaz. The process whereby 
igneous emanations transform granite into greisen 
is called greisening or greisenisation. 
J. S. Flett : Mem. Geol. Surv. (Bodmin & St. Austell), TQOO, 
p. 67. 

Griquaite, Beck, 1907. A phanerocrystalline gar- 

net-diopside rock (with or without olivine or 

phlogopite) occurring as nodular xenoliths in 

kimberlite pipes and dvkes. A variety of Ariegite. 

T. G. Bonney : Proc. Roy. Soc., A., Ixv, iqoo, p. 223. 

P. A. Wagner : The Diamond Fields of S. Africa, 1014, p. 

Grit. - - This term has been used with many different 
connotations : for coarse-grained sandstone ; for 
sands and sandstones, coarse or fine, made up of 
angular grains ; for sandstones with calcareous 
cement ; and for sandstones with grains of con- 
spicuously unequal sizes. Stratigraphically it 
appears in the names of formations so different and 
variable in grade, angularity, and composition as 
Millstone Grit, Coniston Grit, Skiddaw Grit, Pea 
Grit, and Trigonia Grit. By Lyell the term was 
adopted for coarse-grained sandstones, and there 
is now a tendency to restrict it for petrographic 
purposes to the cemented detrital sediments cor- 
responding- in grade to very coarse sand. Manv 
authors, however, prefer to use the term for loose 
or cemented sediments which are " gritty " on 
account of the angularity of the grains. 

Grorudite, Brogger, 1894. - - A microgranitic dyke- 
rock, containing- prisms of aeg-irine, and, when 
porphyritic, having phenocrysts of alkali-felspar 
and aegirine. (Grorud, Christian ?a.) 

W. C. Brogger : Eruftivgest . Krisfiania, i, 1894, p. 6. 


Ground-water. A general term for the water occupy- 
ing the interstices and other openings of rocks 
below the water table ;- Phreatic water. 
For a general classification and discussion of ground-waters, 
see R. A. Daly : Econ. Geol., xii, 1917, p. 487. 

Guano. A phosphatic deposit, formed from the drop- 
pings of sea-fowl in arid regions, which may be 
friable or compact according to its age and the 
degree of alteration it has suffered by weathering. 


Habit. -- A term connoting the sum of the external 
characteristics of a mineral or rock. In its appli- 
cation to rocks the term implies more than struc- 
ture or texture, including also other features which 
control the outward appearance, such as lustre, 
degree of alteration, and fracture. Habit may be 
described broadly by general terms, such as 
cenotypal and paleotypal ; or particularly by terms 
referring to the appearance of well-known types, 
e.g. t tinguaitic habit, aplitic habit, pegmatoid 
habit, etc. 

Halleflinta. -- A term applied to granulose rocks of 
horny aspect which are compact or porphyritic, and 
sometimes banded. The mineral composition, 
quartz, felspar, micas, chlorite, etc., indicates a 
metamorphic origin from quartz-porphyry, rhyolite, 
or corresponding volcanic tuffs. 

Halleflintgneiss. A term formerly used in Sweden 
for rocks that are not called leptites. 

Haloes. See Pleochroic Haloes. 
Haplite. See Aplite. 

Harrisite, Harker, 1908. A phanerocrystalline rock 
composed essentially of black lustrous cleavable 
olivine with anorthite and a little augite ; = 
anorthite peridotite. (Harris, Rum.) 

A. Harker : Mem. Geol. Surv. Scot., 60 (Small Isles), 1908, 
p. 71. 


Hartschiefer. A strongly banded and partly schistose 
rock due to dynamic metamorphism, and asso- 
ciated with other rocks of mylonitic habit, in which 
the alternating- bands have been produced from 
ultramylonite by recrystallisation and metamorphic 
P. Quensel : Bull. Geol. Inst. U-psala, xv, 1916, p. 104. 

Harzburgite, Rosenbusch, 1887. -- A peridotite con- 
sisting- of olivine and orthorhombic-pyroxene ; = 
Saxonite. (Harzburg.) 

Hatherlite, Henderson, 1898. A term originally sug- 
gested for rocks now known as leeuwfonteinite ; 
= anorthoclase-syenite. 

Hauynophyre, Rammelsberg. An analogue of neph- 
elinite, in which the place of nepheline is largely 
taken by haiiyne and nosean. 

Hawaiite, Iddings, 1913. -- A general term for rocks 
of basaltic texture (as contrasted with typical an- 
desite texture), in which the felspar is andesine. 

(Kilauea, Hawaii.) 

Heavy Liquids. A group of heavy organic liquids, 
inorganic solutions, and fused salts (heavy melts] 
used for the determination of the specific gravity 
of mineral particles, or for the separation of 
minerals, having respectively lower and higher 
specific gravities than the liquid used, e.g.. Bromo- 
form, Thoulet Solution, Klein Solution, Mercurous 
nitrate, etc. 

Hedrumite, Brogger, 1890. A leucocratic variety of 
alkali-syenite containing accessory nepheline. 

(Hedrum, S. Norway.) 
W. C. Brogger : Eru-ptivgest. Kristiania, iii, 1898, p. 183. 

Helicitic Structure. A structure of metamorphic 
rocks due to the presence in porphyroblastic con- 
tact minerals of strings of inclusions representing 
an earlier schistosity of the rocks. 

A. Backstrom : Geol. Foren i Stockholm ForhandL, xl, 1918, 
p. 167. 


Hemicrystalline. A term applied to igneous rocks to 
denote that they consist partly of crystals and 
partly of glass or devitrified glass. 

Heptorite, BUSZ, 1904. A melanocratic hauyne-basa- 
nite containing phenocrysts of barkevikite, titan- 
augite and hauyne, in a glassy or analcitic ground- 
mass containing microlites of labradorite. 

(Rhonderfer Thai, Siebengebirge.) 
K. Busz : Neues Jahr., ii, 1904, p. 91. 

Heronite, Coleman, 1899. A dyke rock consisting of 
spheroidal groups of orthoclase in a base of anal- 
cite containing radiating bundles of labradorite 
and, in smaller quantity, aegirine ; since shown to 
be an altered tinguaite. 

(Heron Bay, Ontario.) 

A. P. Coleman : Journ. GeoL, vii, 1899, p. 431;. 
E. A. Barlow : Cong. Geol. Inter., xii, Guide 8, 1913, p. 17. 

Heteromorphic, Lacroix, 1917. -- A term applied to 
rocks of similar chemical composition, but of dif- 
ferent mineral composition ; as, for example, where 
leucite and olivine in one rock may be represented 
by biotite in another. 

A. Lacroix : C.R., clxv, 1917, p. 486; clxx, 1920, p. 23. 
Heumite, Brogger, 1898. A fine grained melanocra- 
tic dyke-rock composed of alkali-felspars, nephe- 
line, and sodalite, with barkevikite, biotite, and 
augite as abundant mafic constituents. 

(Heum, S. Norway.) 
W. C. Brogger : Eru-ptivgest. Kristiania, iii, 1898, p. 90. 

Hexahedrite, Rose. - - A group name for those iron 
meteorites which have a cubic cleavage, and which, 
on being etched, reveal a system of fine lines 
(Naumann Lines) due to twinning parallel to the 
octahedral faces. 

Hiatal Fabric, C./.P. IF., 1906. A variety of inequi- 
granular texture in which the sizes of the crystals 
are not continuously graded, but form a broken 
series, as in most rocks exhibiting porphyritic and 
poikilitic textures. 
J. P. Iddings : Igneous Rocks, I, 1909, p. 198. 


Hillhouse Basalt. Hatch, 1892. A type of the Scot- 
tish' Carboniferous basalts ; characterised by 
numerous micro phenocrysts of olivine and fewer of 
aug-ite, in a fine groundmass in which augite pre- 
dominates ; = Picrite-basalt . 

J. S. Flett : Men?. Geol. Surv. Scot. (Edinburgh), IQIO, 
p. 316. 

Hirnantite, Cope, 1915. A variety of albite-kerato 
phyre, or albitised tholeiite, containing- laths of 
sodic plagioclase embedded in an interstitial base 
of chlorite, with smaller amounts of calcite, quartz, 
leucoxene and haematite. 

(Craig-ddu Hirnant, Berwyn Hills.) 
T. H. Cope : Proc. Liverpool Geol. Soc. (Cope Memorial 
Vol.), 1915, p. 79. 

Hogbomitite, Gavelin, 1917. - - See Magnetite- 

Holocrystalline. - - A term applied to igneous rocks 
completely made up of crystals. 

Hololeucocratic, Holomelanocratic, Lacroix, 1902. 

Terms applied to facies of igneous rocks, or to 
members of a series of related rocks, which are 
almost completely composed of lignt or dark 
minerals respectively. 

A. Lacroix : Now, Arch, du Mus. d'Hist. Nat., i, TQ02, 
p. 161. 

Holyokeite, Emerson, 1902. A variety of albite-da- 
base containing 70 per cent, albite, 9 per cent, 
orthoclase, and 16 per cent, calcite, with smaller 
amounts of accessory minerals. 

(Holyoke, Mass., U.S.A.) 

B. K. Emerson : Journ. Geol., x, 1902, p. t;io. 

Homoeoblastic, Becke, 1903. A term used instead of 
equigranular and applied to metamorphic rocks to 
indicate that the texture so described is due to 
recry stall i sat ion. 

Hornblende-Schist. A schist in which hornblende is 
the dominant mineral : plagioclase and sometimes 
quartz being- the chief felsic constituents. With 


loss of schistose structure the rock passes into 

hornblende-gneiss and amphibolite. 
J. J. H. Teall : Q.J.G.S., xli, 1885, p. 133. 
i'. G. Eonney : Q./.G.S., lii, 1896, p. 18. 
J. S. Flett : Mem. Geol. Surv. (Lizard), 1912, p. 44. 

Hornblendite, Dana, 1880. A phanerocrystalline ig- 
neous rock essentially composed of hornblende. 
Olivine-hornblendite is the passage rock to horn- 

Hornfels. A contact metamorphosed rock, usually of 
speckled granular appearance, but not typically- 
schistose, nor strictly granulose, consisting essen- 
tially of quartz, micas, and felspars, with or with- 
out garnet, andalusite, or cordierite, and more 
rarely pyroxene or amphibole. Any cleavage or 
incipient schistosity possessed by the parent rock 
is obliterated by a new structure which may be 
described as maculose. 

J. S. Flett : Mem. Geol. Surv. (Dartmoor), 1912, p. 45. 

H. Backhand : Geol. Foren i Stockholm Forhandl., xl, 1918, 
p. 184. 

Hornstone. A general term for compact, tough, sili- 
ceous rocks having a splintery or sub-conchoidal 
fracture ; distinguished from flint and chert by 
greater opacity in thin flakes and the presence of 
a veined, banded, or other parallel structure such 
as lamination or cleavage. 

Howardite, Rose, 1863. - - An achondritic meteorite 
containing bronzite, olivine, and anorthite, with 
little or no iron. 

Hudsonite, Cohen. - The term originally suggested 
for rocks now known as Cortlandtite. The latter 
term is generally adopted as hudsonite had pre- 
viously been given to a variety of pyroxene. 

(Hudson R., New York.) 

Hullite. A soft dark substance occurring as inter- 
stitial matter and amygdaloidal infillings in Antrim 
basalts. It is of the same nature as palagonite, 


but differs from the latter in having a low specific 
gravity, viz., 1.76. 

(Carnmoney Hill, near Belfast.) 

G. A. J. Cole : Rep. Belfast Nat. Field Club, 1894-5, p. i. 

J. J. H. Teall : Q.J.G.S., liii, 1897, pp. 485-6. 
Humic Coals, Potonie, 1904. -- A group of coals, in- 
cluding the ordinary bituminous varieties, which 
have been formed from accumulations of vegetable- 
debris that have maintained their morphological 
organisation with little decay. 

Marie C. Slopes & R. V. Wheeler : The Constitution of Coal, 
1918, p. 19. 

Hunne Diabase, Tornebohm, 1877. A type of quartz- 
dolerite containing hornblende, biotite and a little 
quartz, in addition to plagioclase and a pale augite 
(sahlite). Interstitial chloritic matter is oiten 
present, and the type is frequently somewhat 
porphyritic in aspect. Cf. Konga Diabase. 

(Hunneberg, Sweden.) 

Hyalo-. A prefix added to certain rock names to sig- 
nify a glassy rock of corresponding chemical com- 
position, e.g., hyalo-basalt. 

Hyalomelane, Haussmann, 1847. A name given to 
basaltic glass at a time when the latter was con- 
sidered to be a definite mineral species. 

Hyalo-ophitk Texture, Polenov, 1899. A texture re- 
sembling ophitic texture, in which the spaces of an 
open network of felspar laths are occupied by 
glass ; a limiting case of intersertal texture. 

Hyalopilitic. A groundmass texture in which laths 
or microlites of felspar are interwoven (as in a felt) 
with glass occupying the interstices between 
adjacent crystals. 

Hybrid, Durocher, 1857. A term originally applied to 
" intermediate " rocks at a time when they were 
regarded as the products of composite magmas 
derived from the admixture of the " trachytic " and 
" pyroxenic " magmas of Bunsen. By Harker, 
1904, the term is adopted for abnormal igneous 


rocks, of which Marscoite is an example, formed 
by the mixture of two magmas, or by the assimila- 
tion of a rock already consolidated by the magma 
of a later intrusion. 

A. Marker : Mem, Geol. Surv. (Tert. Ig. Rocks, Skye), 1904, 

p. 181. 
Nat. Hist. Ig. Rocks, 1909, p. 333. 

Hydatogenesis. The process whereby mineral depo- 
sits are formed from magmatic solutions rich in 
water. The term is also employed by some au- 
thors for all deposits formed from aqueous solu- 
tion whether the waters be magmatic, vadose, or 

HydatogenoilS, Renevier, 1880. -- A term applied to 
chemical deposits of aqueous origin, including 
vein deposits. 

Hydrpthermal. A term applied to magmatic emana- 
tions rich in water; to the processes in which they 
are concerned ; and to the rocks or ore-deposits, 
alteration products, and springs produced by them. 

G. W. Morey & P. Niggli : Journ. Am. Chem. Soc., xxxv, 

1913, p. 1086. 
E. A. Stephenson : Journ. Geol., xxiv, 1916, p. 180. 

Hypabyssal. A general term applied to minor intru- 
sions, such as sills and dykes, and to the rocks of 
which they are made, to distinguish them from 
volcanic rocks and formations on the one hand, 
and " plutonic " rocks and major intrusions such 
as batholiths on the other. 

Hyperite, Elie de Beaumont. A term at first synony- 
mous with Norite, now extended to include some- 
what granular hypersthene-felspar rocks with or 
without augite, diallage, or garnet. 
J. J. H. Teall : Mem. Geol. Surv. (Sil. Rocks, Scotland), 1, 
1899, P- 6l 3- 

Hypersthenite. A rock composed wholly or almost 
wholly of hypersthene. Small amounts of other 
pyroxenes, plagioclase, or olivine may be present. 


Hypidiomorphic, Rosenbusch. -- A general term ap- 
plied to those forms of igneous rock-minerals 
which are bounded only in part by their character- 
istic crystal faces, i.e., for forms intermediate be- 
tween idiomorphic and cdlotriomorphic ; = Sub- 
hedral; = Hypautomorphic. 

Hypidiomorphic Texture. A texture of igneous rocks 
due to the development of the greater proportion of 
the minerals in crystals having hypidiomorphic 

Hypocrystalline. -- A term applied to igneous rocks 
made up partly of crystals and partly of glass. 

Hypogene, Lyell, 1833. A general term intended to 
include both plutonic and metamorphic classes of 
rocks, that is, for rocks formed within the earth. 
By A. Geikie, 1879, tne term was use d for geolo- 
gical processes originating within the earth, and 
if it were applied to rocks in this sense, it would 
therefore include volcanic rocks, which were inten- 
tionally excluded by Lyell from his hyogene rocks. 
Cf. Epigene; Endo genetic. 

Hysterobase, Lassen, 1888. A variety of diabase con- 
taining plagioclase, quartz, biotite, and brown 
hornblende, the latter paramorphic after augite. 

Idioblast, Becke, 1903. -- A term applied to pseudo- 
idiomorphic crystals, such as garnet, occurring in 
metamorphic rocks. An idioblast may be high in 
the crystalloblastic order of the minerals present, 
but it has no significance in relation to order of 
crystallisation, as would be the case in igneous 

Idiomorphic, Rosenbusch. A general term applied to 
the forms of igneous rock-minerals which are com- 
pletely bounded by the crystal faces peculiar to the 
species ; = Euhedral ; = Automorphic. 


Ijolite, Ramsay, 1891. -- A phanerocrystalline rock 
essentially composed of nepheline and aegirine- 
augite or other pyroxene free or nearly free from 
normative plagioclase. Cf. Fasinite. 

(Ijola, Finland.) 
V. Hackman : Bull. Comm. geol. Finlande, No. n, 1900. 

Ijussite, Rakovski, 1911. -- A variety of teschenite- 
pyro'xenite containing abundant titanaugite and 
barkevikite, with small amounts of bytownite, 
anorthoclase and analcite. (Ijuss R., Siberia.) 

J. Rakovski : Trans, Mus. Pet. Or. Ac. Sci. St. Pet., v, 
1911, p. 256. 

Ilmenite-norite, Kolderup, 1896. A variety of norite 
(hypersthene and labradorite) with a high percen- 
tage of ilmenite varying in different parts of the 
rock-mass from 20 to 80 per cent. 

Ilmenitite, Kolderup, 1896. A facies of ilmenite- 
norite consisting predominantly of ilmenite. 

C. F. Kolderup : Bergen Mus. Aarb., v, 1896, p. 178. 

Imandrite, Ramsay, 1894. A rock composed of 
quartz and albite, due to interaction between a 
nepheline-syenite magma and graywacke. 

(Umptek, Kola.) 
W. Ramsay & V. Hackman : Fennia, xi, 1894, p. 74. 

Impregnation. A term expressing the irregular dis- 
tribution of introduced mineral matter through a 
previously formed rock; contrasted with dissemi- 
nation which expresses distribution without 
implication as to order of deposition. 

Impsonite, Eldridge, 1901. A variety of asphaltite 
having a specific gravity of 1.175, characterised by 
a hackly fracture, and by being soluble in carbon 
disulphide to the extent of about 35 per cent. 

G. H. Eldridge : U.S.G.S., 22nd Ann. Re-p., Ft. i, 1901, 
p. 221. 

Inclusion. A general term for foreign bodies (gas, 
liquid, glass, or mineral) enclosed by minerals ; 
also extended in its English usage to connote en- 



closures of rocks and minerals within igneous 

rocks, such as cognate and accidental inclusions. 

It is, however, desirable to distinguish inclusions, 

enclosures, and segregations (q-v.). 
J. A. Smythe : Geol. Mag., 1914, p. 244. 
S. Powers : Journ. Geol., xxiii, 1915, p. i. 

Indurated. A term technically restricted to compact 
rocks that have been hardened by the action of 

Ingenite, Forbes, 1867. A general term for igneous 
rocks "born, bred, or created within or below." 
By Kinahan, 1873, the term was extended to in- 
clude metamorphic rocks as well as the igneous 
rocks alone considered by Forbes. Cf. Derivate. 

Injection Gneiss. A gneiss whose banding is wholly 
or partly due to the lit-par-lit, or interlaminar, in- 
jection of granitic magma into schistose, fissile, 
or otherwise penetrable rocks ; = (in part) Com- 
posite Gneiss. 

Inninmorite, Thomas & Bailey, 1915. A porphyri- 
tic rock containing phenocrysts of plagioclase 
(labradorite to anorthite) and augite, in a ground- 
mass of more sodic plagioclase, augite, and abun- 
dant glass. (Inninmore, Morven.) 
E. M. Anderson. & E. G. Radley : Q.J.G.S., Ixxi, 1916, p. 205. 

Intercalate. A term applied generally to a body of 
one kind of material interlaminated with another ; 
and particularly to lamellar inclusions of one mine- 
ral in another, the former being orientated more or 
less exactly in planes related to the crystal struc- 
ture of the latter, e.g., in perthite (intercalates of 
plagioclase in orthoclase), and in certain minerals 
characterised by schiller structure. 

Intergranular, Evans, 1916. A texture characteristic 
of holocrystalline basalts and doleritic rocks, due 
to the aggregation of grains of augite (not in opti- 
cal continuity, as in sub-ophitic texture) between 
felspar laths arranged in a network that may be 
diverse, sub-radial, or sub-parallel; distinguished 


from inters e rial by the absence of interstitial glass, 
or other substances that take the form of the inter- 
stitial spaces. Cf. Granulitic Texture. 
A. Holmes : Min. Mag., xviii, 1918, p. 191. 

Intersertal, Zirkel, 1870. A texture characterised by 
the insertion between divergent laths of felspar of 
glass, palagonite, chlorite, or other primary or 
secondary minerals that take the form of the inter- 
stitial spaces. In intersertal basalts, the grains 
of augite rarely occupy the wedge-shaped spaces 
completely, continuity being established by a 
mesostasis of glass or its alteration products. 

Intratelluric, Rosenbusch. A term applied to the 
period of crystallisation of a magma anterior to its 
effusion as a lava, and represented in many vol- 
canic rocks by phenocrysts formed under com- 
paratively deep-seated conditions. Such crystals, 
belonging to an earlier generation than the 
groundmass, are also described as intratelluric. 

Isenite, Bertels, 1874. A felspathoid-bearmg variety 
of hornblende-trachyandesite, having phenocrysts 
of andesine, soda-microline, hornblende and 
biotite, in a groundmass of oligoclase, orthoclase, 
and nosean, with small amounts of augite, apatite 
and iron-ores. (Nassau.) 

IsomorphoilS. A term applied to two or more 
minerals or other crystalline bodies which form an 
isomorphous series when they are related by close 
similarity of chemical constitution, and crystallise 
in the same class of the same system of symmetry, 
developing the same forms with angles that differ 
by not more than, a few degrees. Such minerals 
can form intimate crystalline mixtures or solid 
solutions (e.g. , albite and anorthite), in which the 
physical properties change continuously with the 
composition. Certain minerals are imperfectly 
isomorphous (e.g., atbite and orthoclase) when one 


or more of the above criteria fails to hold, and 
only a limited amount of one mineral is capable of 
being molecularly dispersed through the other. 

A. L. Day & E. T. Allen : Am. Journ. Sci., xix, 1905, p. 93 

A. L. Day : Bull. GeoL Soc. Am., xxi, 1910, p. 147. 

A. E. II. Tutton : Crystalline Structure and Chemical Con- 
stitution, 1910, p. 124. 

Issite, Duparc & Pamfil, 1910. A melanocratic 
dyke rock containing hornblende, with a smaller 
quantity of green pyroxene and a variable but al- 
ways subsidiary amount of labradorite ', = melano- 
cratic hornblende- gabbro, or felspathic hornblen- 

L. Duparc & P. Pamfil : C.R., cli, 1910, p. 1136; Bull. Soc. 

Min. France, xxxiii, 1910, p. 351. 

Itabirite, Eschivege. A variety of quartzite contain- 
ing abundant iron-ore minerals, with accessory 
oligoclase and muscovite. (Itabira, Brazil.) 

Itacolumite, Humboldt. - - A schistose and flexible 
variety of quartzite containing micaceous minerals 
(mica, chlorite, talc) in addition to the chief con- 
stituent, quartz. (Mt. Itacolumi, Brazil.) 

R. D. Oldham : Rec. GeoL Surv. India, xxii, 1889, p. 51. 

G. W. Card : GeoL Mag., 1892, p. 120. 

Invernite, Watts, 1895. A holocrystalline intrusive 
rock of granitic aspect containing phenocrysts of 
orthoclase and fewer of plagioclase in a ground- 
mass consisting of stumpy idiomorphic felspars 
(mostly orthoclase but in part plagioclase), 
sparsely distributed hornblende or mica, and in- 
terstitial quartz. 

W. W. Watts : In Guide to the Collections of Rocks and 
Fossils, Gecl. Surv. Ireland, 1895, p. 93. 

JaCUpirangite, Derby, 1891. -- A term applied to a 
melanocratic series of igneous rocks of varying 
composition, the characteristic minerals being 
purple titanaugite, nepheline, and magnetite or 


titanoferrite. The chief types range from ijolite- 
like rocks (pyroxene-nepheline rocks with some 
biotite and olivine) to alkali-pyroxenites, and from 
each of these to varieties rich in magnetite. 

(Jacupiranga, Brazil.) 
H. S. Washington : Journ. Geol., ix, 1901, p. 620. 

Jadeitite. A rock consisting of the alkali-pyroxene 
jadeite associated with small amounts of felspar or 
felspathoid, and probably derived from alkali- 
igneous rocks by high-pressure metamorphism. 

Jasperisation. The alteration of rocks, igneous or 
sedimentary, into banded jaspilite-like rocks by 
metasomatic processes in which iron-oxides and 
silica are successively introduced. 

A. E. V. Zealley : Trans. Geol. Soc. S. Africa, xvi, 1918, 
P- 43- 

Jasperoid. A term sometimes used for limestones and 
calcareous rocks., in which the carbonates have 
been replaced by fine-grained quartz aggregates or 
chalcedony. Rocks of this kind are generally 
grey, and chert-like in appearance, and they are 
often developed as the gangue of metasomatic 
sulphide deposits, particularly those of the silver- 
lead type. 

Jaspilite. A term applied to rocks composed of inter- 
banded layers respectively rich in silica (quartz or 
chalcedony) and iron-oxides (magnetite, haematite, 
etc.). The chert-like bands have a red colour 
owing to the inclusion of flakes of haematite. 
Variable amounts of ferruginous amphiboles are 
generally present, and the rocks are not only 
conspicuously banded, but are often contorted and 
C. R. Van Hise & C. K. Leith : U.S.G.S., Mon. Hi, 1911, 

PP- 124, 464, 466. 

C. R.- Van Hise : Journ* and Proc. Roy. Soc. West Aust.> 
ii, p. 23. 


Jedburgh Basalt, Watts, 1897. A type of the Scot- 
tish Carboniferous basalts ; characterised by in- 
conspicuous phenocrysts of olivine and plagioclase 
in an ophitic to microlitic groundmass, to which 
augite is almost always restricted. 
E. B. Bailey : Mem. Geol. Surv. Scot. (Glasgow District), 

1911, p. 138. 
G. W. Tyrrell : Trans. Geol. Soc. Glasgow, xiv, 1912, p. 226. 

Jet. A hard coal-black variety of lignite, showing the 
structure of coniferous wood under the microscope. 
Mem. Geol. Surv. S-pec. Re-p., Mineral Resources of Great 
Britain, vii, 1918. 

Josefite, Szadeczhy, 1899. An altered microgranular 
dyke rock consisting of augite and olivine, with 
abundant serpentine and calcite. (Assuan.) 

Jtimillite, Osann, 1906. A fine-grained porphyritic 
rock containing phenocrysts of orthoclase (with 
poikilitic inclusions of olivine), phlogopite and 
soda-pyroxenes and amphiboles in a matrix of 
soda-amphibole and leucite, with accessory apatite 
and titanoferrite. (Jumilla, Murcia, Spain.) 

A. Osann : Festschrift H. Rosenbusch, 1906, p. 263. 

Juvenile, Suess, 1902. A term applied to water and 
other volatile materials that are known to be mag- 
matic emanations of primary endogenetic origin. 
Those of secondary endogenetic origin occurring 
as emanations derived from country rock are dis- 
tinguished by Daly as Resurgent. 
R. A. Daly : Econ. Geol., xii. 1917, p. 489. 


Kaiwekite, Marshall, 1906. An olivine-bearing variety 
of alkali-trachyte or trachyandesite, approximately 
representing the volcanic equivalent of laurvikite. 
The rock contains phenocrysts of anorthoclase, 
titanaugite mantled with segirine, barkevikite, and 
olivine, in a groundmass of oligoclase with small 
amounts of pyroxene and magnetite. 

(North Head, Otago, N.Z.) 
P. Marshall : Q.J.G.S., Ixx, 1914, p. 390. 


Kakirite, Svenonius. A megascopically sheared and 
brecciated cataclastic rock in which fragments of 
the original material are surrounded by innumer- 
able gliding surfaces in which intense granulation 
and some recrystallisation have taken place. 

(Lake Kakir, Swedish Lapland.) 
P. Quensel : Bull. Geol. Inst. Upsala, xv, 1916, p. 100. 
Kakortokite, Ussing, 1911. A banded nepheline- 
syenite containing leucocratic layers rich in felspar 
and nepheline (white), others rich in eudialite and 
nepheline (red), and melanocratic layers rich in 
aegirine and arfvedsonite (black). 
N. V. Ussing : Medd. om Gronland, xxxviii, 1912, p. 177. 

Kankar. A vernacular Indian term for stone; now 
restricted to concretionary masses of calcium car- 
bonate occurring in alluvium ; = Kunkar. 

Kaolin. Kaolin is a white, or slightly stained, clay, 
due to the decomposition of a highly felspathic 
rock, and therefore also* containing a variable pro- 
portion of other constituents! derived from the 
parent rock. The clay-substance itself is 
essentially a hydrated silicate of alumina, and to 
this material the name kaolinite is frequently 
given. The word kaolin is derived from the 
Chinese kuling, meaning " high ridge," the ridge 
referred to, near Jaochau Fu, having been wrongly 
considered to be the site of an, important deposit 
which actually lies at the foot of the ridge. See 
J. A. Howe : Mem. Geol. Surv. (Kaolin, China Clay and 

China Stone), 1914. 

W. R. Jones : Clays of Economic Im-portance in the F .M.S., 
Govt. Press, Kuala Lumpur, 1915. 

Kaolinisation. The processes whereby felspars, and 

other alumino-silicates, are altered to kaolin. 
J. A. Howe : Mem. Geol. Surv. (Kaolin, China Clay and 
China Stone), 1914, p. 135. 

Karite, Karpinsky, 1904. A variety of grorudite con- 
taining about 50 per cent, of quartz. 

(R. Kara, Siberia.) 


Kassaite, Lacroix, 1918. A microlitic dyke-rock con- 
taining- phenocrysts of hauyne, barkevikite, augite 
and labradorite in a groundmass of hornblende and 
felsic minerals. (Los Archipelago.) 

A. Lacroix : C.R., clxvi, 1918, p. 542. 

Kata-, Grubenmann, 1907. A prefix used as a qualifier 
to the group-names suggested by Grubenmann for 
metamorphic rocks, to indicate that the type so 
distinguished belongs to the deepest zone of meta- 
morphism. In this, zone the distinctive physical 
conditions are very high temperature and hydro- 
static pressure, and comparatively feeble stress, 
and the rocks characteristically produced include 
biotite-, sillimanite-, cordierite-, garnet-, and 
pyroxene-gneiss, granulites, and eclogite. Cf. 
Epi-j and Meso-. 

U. Grubenmann : Die Kristallinen Schiefer, II, 1907, pp. 
21, 172. 

Kataclastic. See Cataclastic, Kjerulf. 

KatagneisS. A term applied to gneisses, amphibolites, 
etc., considered to have been formed in the deep- 
est zone of metamorphism, where high tempera- 
ture is a controlling factor, and high hydrostatic 
pressure dominates over shearing stress. (Note 
the different sense in which kata- is used in the 
following term.) 

Katamorphism, Van Hise, 1904. - - The alteration of 
rocks by weathering and cementation, the charac- 
teristic changes involving the production of simple 
compounds from more complex minerals. 
C. R. Van Hise: U.S,G.S. Man., 47, 1904. 
C. K. Leith & W. J. Mead : Metamorphic Geology, 1915. 

Katzenbuckelite, Osann, 1903. A porphyritic rock of 
tinguaitic habit having phenocrysts of nepheline, 
nosean, biotite, and olivine, in a glassy or crypto- 
crystalline groundmass containing minute crystals 
of nepheline, leucite, orthoclase, biotite and soda- 
pyroxenes and amphiboles. 

(Katzenbuckel, Odenwald, Baden.) 
A. Osann : Tschermak's Min. Pet. Mitt., xxi, 1903, p. 365. 


Kauaiite, Iddings, 1913. A coarse gabbro-like rock 
containing- augite and olivine and zoned felspars 
ranging from calcic labradorite in the inner to 
alkali-felspar in the outer zones ; = olivine-augite- 
diorite. (Hawaiian Is.) 

W. Cross : U.S.G.S., Prof. Pap., 88, 1915, p. 15. 

Kedabeldte, Fedorof, 1901. A garnetiferous variety 
of gabbro or eucrite, in which the plagioclase is 
anorthite. (Kedabek Caucasus.) 

Kelyphitic, Schrauf, 1882. - - A term applied to the 
" rims " or " borders," composed of microcrystal- 
line aggregates of pyroxene or amphibole, which 
sometimes appear around olivine where it would 
otherwise be in contact with plagioclase, or around 
garnet where it would otherwise be in contact with 
olivine or other mag-nesium-rich minerals. Bonney 
suggests that the term be restricted to occurrences 
of secondary origin, applying the term Corona to 
those that are primary. 

J. J. Sederholm : Bull. Comm. Geol. Finlande, No. 48, 1916, 
P- 47- 

Kentallenite, Hill & Kynaston, 1900. A phanero- 
crystalline rock consisting essentially of olivine 
(dusty in thin section), pale-green augite, biotite, 
plagioclase, and orthoclase. Some varieties may 
be regarded as melanocratic olivine-monzonite, but 
in others orthoclase is inconspicuous or occultl 

(Kentallen, Loch Linnhe.) 
J. B. Hill & K. Kynaston : Q.J.G.S., Ivi, 1900, p. 531. 

Kenyte, Gregory, 1900. A variety of alkali-trachyte, 
containing phenocrysts of anorthoclase in a hyalo- 
pilitic or trachytic base. ^Egirine-augite is pre- 
sent, and, in some varieties, olivine. 

(Mt. Kenya, B.E.A.) 
J. W. Gregory : Q.J.G.S., Ivi, 1900, p. 205. 
G. T. Prior : Min. Mag., xiii, 1902, p. 246. 
Keralite, Cordier, 1868. A variety of hornfels having 

quartz and biotite as its essential minerals. 
Keratophyre, Gumbel, 1874. - - A soda-porphyry or 
trachyte containing albite-oligoclase or anortho- 


clase in an orthophyric or felsitic groundmass ; 
pyroxenes, often altered to chlorite, epidote, 
etc., may be present. 

A. H. Cox : Re-p. Brit. Assoc. (Birmingham, 1913), 19145 p. 

Kersantite, Deles se, 1851. A dioritic lamprophyre 
characterised by biotite and plagioclase. 


Khagiarite, Washington, 1913. A black vitreous 
variety of pantellerite containing phenocrysts of 
soda-microcline, diopside, segirine-augite, and 
cossyrite, in a groundmass of brown glass having 
a flow texture due to the arrangement of micro- 
lites or crystallites. = Hyalo-pantellerite. 
H. S. Washington : Journ. GeoL, xxi, 1913, p. 708. 

Khondalite Series, Walker, 1902. A series of meta- 
morphic rocks (named after the Khonds of India, 
in whose country they occur), consisting of garnet- 
quartz-sillimanite rocks with garnetiferous quartz- 
ites, graphite-schists and calciphyres. 
T. L. Walker : Mem. Geol. Surv. India, xxxiii, 1902, p. n. 

Kidlaw Basalt, Bailey, 1910. A type of the Scottish 
Carboniferous analcite-basalts ; characterised by 
numerous microphenocrysts of olivine and augite 
in a groundmass notable for the relative abund- 
ance of orthoclase and biotite and the presence of 
analcite in large poikilitic crystals. 

E. B. Bailey : Mem. Geol. Surv. Scot. (East Lothian), 1910, 
pp. 105-113. 

Kieselguhr. See Diatomite. 

Killas. A Cornish mining term for the altered, 
schistose, or hornfelsic rocks in contact with 
granite, and often considerably modified by emana- 
tions from the latter. 

Kilsyth Basalt, Watts, 1897. A variety of the Markle 
type (q.v.) of the Scottish Carboniferous basalts, 
characterised by sub-ophitic texture. 


Kimberlite, Carvill Lewis, 1887. A brecciated biotite- 

peridotite, occurring in the diamond-pipes of South 

Africa. (Kimberley.) 

P. A. Wagner : The Diamond Fields of S. Africa, 1914, 

p. 78. 

D. Draper & W. H. Goodchild : Mining Journ.. cxiii, 1916, 
PP- 357, 3 6 S- 

Kinne Diabase, Tornebohm, 1877. A type of olivine- 
diabase containing intersertal chloritic matter and 
secondary quartz. 

Kinzigite, Fischer, 1860. A coarsely granulose rock 
formed by the metamorphism of sedimentary rocks 
of appropriate composition, and essentially com- 
posed of garnet and biotite, with varying amounts 
of quartz, orthoclase, oligoclase, muscovite, 
cordierite, or sillimanite. (Kinzig-, Schwarzwald.) 

Klein Solution. A yellow aqueous solution of cad- 
mium boro-tungstate, somewhat viscous when 
saturated, having a maximum specific gravity of 
W. B. D. Edwards : Geol. Mag., 1891, p. 273. 

Knotted Schist or Knotenschiefer. See Spotted 

Kodurite, Fermor, 1907. The type rock of the Ko- 
durite Series, composed of potash felspar, spandite 
(a garnet intermediate between spessartite and 
andradite), and apatite. 

(Kodur Mines, Vizagapatam, India.) 
L. L. Fermor : Rec. Geol. Surv. India, xlii, 1912, p. 208. 

Kodurite Series, Fermor, 1907. A series of rocks of 
uncertain but probably igneous origin, associated 
with the Archaean complex of Madras, and ranging 
from quartz-orthoclase rocks through Kodurite to 
spandite-rock and manganese-pyroxenites. 
L. L. Fermor : Mem. Geol. Surv. India, xxxvii, 1909, p. 

Kohalaite, Iddings, 1913. A general term for oligo- 
clase-andesites. (Kohala Mt. , Hawaiian Is.) 

Kolm. A variety of coal occurring locally as lenticles 
in Swedish alum-shales, and containing about 30 


per cent, of ash, which is remarkable for its high 
content of rare metals, including- uranium and 

Konga Diabase, Tornebohm, 1877. A type of grano- 
dolerite containing calcic labradorite laths and in- 
tergranular augite (sahlite) and orthorhombic 
pyroxene, in a microgranitic interstitial mass of 
quartz and orthoclase. Cf. Hunne diabase. 

(Konga, Sweden.) 

Koswite, Duparc, 1902. -- A variety of olivine-pyro- 
xenite containing diopside as its chief constituent 
with olivine in moderate amount, and magnetite 
acting as an interstitial cement. 

(Koswinsky, N. Urals.) 

L. Duparc & P. Pamfil : Bull. Soc. Min. France, xxxiii, 
1910, p. 251. 

Krablite, Forchhammer, 1832. A variety of crystal- 
tuff containing abundant sanidine, with plagio- 
clase, augite, and quartz in smaller proportions. 

(Mt. Krabla, Iceland.) 

Krageroite, Brogger, 1904. An albite-aplite in which 
the place of quartz is largely taken by rutile ; = 
Kragerite. (Kragero, S. Norway.) 

T. L. Watson : Am. Jottrn. Sci., xxxiv, 1912, p. 509. 

Kulaite, Washington, 1894. A nepheline- or leucite- 
bearing trachydolerite in which hornblende is the 
dominant mafic mineral ; varieties in which ortho- 
clase cannot be recognised resemble tephrite. 

(Kula Devit, Lydia, Asia Minor.) 
H. S. Washington : Journ. GeoL, viii, 1900, p. 610. 

Kullaite, Hennig, 1899. A variety of diabase contain- 
ing red phenocrysts of plagioclase and microcline. 

(Kullen, Sweden.) 
Kunkar. See Kankar. 

Kuskite, Spurr, 1900. A term applied to quartz- or 
adamellite-porphyry containing primary scapolite. 

(Kusko R., Alaska.) 

J. E. Spurr: Am. Journ. Sci., x, 1900, p. 315; U.S.G.S., 
zoth Ann. Re-p., Pt. vii, 1900, p. 221. 


Kvellite, Brogger, 1898. A porphyritic syenite-lam- 
prophyre containing olivine, barkevikite, lepido- 
melane, apatite and magnetite in a groundmass of 
anorthoclase laths. Cf. Tjosite. 

(Near Lougental, Christiania District.) 

Kylite, Tyrrell, 1912. A melanocratic olivine-essexite 
with abundant labradorite, titanaugite, and oli- 
vine, and small amounts of nepheline and analcite. 
Cf. Luscladite. (Kyle district, Ayrshire.) 

G. W. Tyrrell : Geol. Mag., 1912, p. 121. 

Kyschtymite, Moroziewicz, 1897. A phanerocrystal- 
line rock composed of anorthite, biotite, and 
corundum, and smaller amounts of green spinel, 
zircon and apatite. (Kyschtym, Urals.) 

A. E. Barlow : Geol. Surv. Canada, Mem. 57 (Pub. No. 
1022), 1915, p. 231. 

Laanilite, Hackman, 1905. A coarse-grained peg- 
matoid rock of which the essential constituents are 
garnet, biotite, quartz and iron ores. 

(Laanila, Finnish Lapland.) 

Labile, Ostwald, 1897. A term describing the condi- 
tion of a supersaturated solution in which the con- 
centration at any given temperature is sufficiently 
high to ensure rapid separation of the solute, even 
in the absence of the solid phase. 

Labradite, Turner, 1900. A phanerocrystalline rock 
composed almost entirely of labradorite. 

Labradorite, Senft, 1857. As a rock name, this term 
is applied by French authors to leucocratic basalts 
rich in the mineral labradorite (Fr. labrador) ; by 
Russian authors it has been used for leucocratic 
varieties of gabbro or norite, i.e., for anorthosite. 

Laccolith, Gilbert, 1880. A dome-shaped intrusion 
with both floor and roof concordant with the 


bedding planes of the invaded formations, the roof 
being arched upwards as a result of the intrusion. 
W. Cross: U.S.G.S., i^th Ann. Rep. (1892-3), ii, 1894, 
p. 165. 

Lakarpite, TSrnebohm, 1906. A phanerocrystalline 
rock composed of microcline, oligoclase, and 
soda-amphibole ; aegirine or rosenbuschite may 
also be present. (Korra Karr, Sweden.) 

A. E. Tornebohm : Sveriges Geol. Unders., Ser. C, No. 199, 
1906, p. 54. 

Lamprophyre, G umbel, 1887. - - A general term for 
those facies of holocrystalline dyke-rocks which 
differ from the normal types containing the same 
essential minerals by the marked abundance of 
their mafic minerals, and the frequent presence of 
alteration products, especially calcite and those 
derived from the felspars.; e.g. , Minette and 

A. Harker : Geol. Mag., 1892, p. 199. 

T. S. Flett : Trans. Roy. Soc. Edin., xxxix, 1900, p. 865. 
J. Morrison : Q.J.G.S., Ixxiv, 1918-19, p. 116. 

Landscape Marble. A popular descriptive term ap- 
plied to an argillaceous limestone of Liassic age, 
found near Bristol (Gotham stone), and charac- 
terised by the presence of conspicuous arborescent 

B. Thompson : Q.J.G.S., 1, 1894, p. 393. 

Lapilli. - - Volcanic ejectamenta consisting of frag- 
ments of lava of rounded or irregular shape, vary- 
ing in size from that of a pea to that of a walnut. 

Lassenite, Wadsworth, 1891. A term proposed for 
fresh trachyte-glass, altered forms being termed 
metabolite. (Lassen Peak, California.) 

Latent Heat. Latent heat is the amount of heat ab- 
sorbed or emitted by i gram of a substance at con- 
stant pressure and constant temperature during a 


change of state. The various types of change are 
distinguished as follows : 

Latent heat of evaporation for the change 

Latent heat of sublimation for the change 


Latent heat of ftision for the change solid- 

Latent heat of solution for the change solute- 

Latent heat of transition for the change solid- 

Laterite, Buchanan, 1807. A residual deposit, often 
concretionary, formed as a result of the decomposi- 
tion of rocks by weathering and ground-waters, 
and consisting essentially of hydrated oxides of 
aluminium and iron, which may be crystalline or 
amorphous. ^ 

L. L. Fermor : Geol. Mag., 1911, p. 454, p. 507, p. 559; 1915, 

p. 28, p. 77, p. 123. 
J. M. Campbell : Mining Mag., xvii, 1916, pp. 67, 120, 171, 


Lateritic Constituents, Fermor, 1911. -- A term ap- 
plied to the hydroxides and oxides of iron, alumi- 
nium, titanium and manganese ; these, and espe- 
cially the first two, being the essential constituents 
of late rite. 

Lateritite, Fermor, 1911. - - A detrital and recon- 
structed form of laterite. 

Lateritoid, Fermor, 1911. A lateritic rock formed by 
the metasomatic replacement of some other rock 
at its outcrop. 

Latite, Ransome, 1898. An andesitic rock of mon- 
zonitic composition containing orthoclase as an es- 
sential constituent in addition to plagioclase ; 
= tr achy ande site. 

Laugenite, Iddings, 1913. A general term for oligo- 

clase-diorites. (Laugendal, Norway.) 

Laurdalite, Brogger, 1890. A variety of nepheline- 

syenite with rhombic anorthoclase and any of the 


following minerals : pyroxene, amphibole and 
biotite ; olivine-bearing varieties also occur. 

(Laurdal, Norway.) 

W. C. Brogger : Eru-ptivgest. Kristiania, iii, 1898, p. 7. 
Laurvikite, Brogger, 1890. A variety of alkali-syen- 
ite composed essentially of rhombic anortho- 
clase, aegirine-augite and biotite. 

(Laurvik, Christiania.) 

W. C. Brogger : Zeit. /. Kryst. u. Min., xvi (i), 1890; p. 28. 
Lavialite, Sederholm, 1899. A metamorphic rock 
with relict phenocrysts of labradorite, probably 
derived from a basaltic rock or tuff. The pheno- 
crysts are penetrated by alteration passages con- 
taining quartz, microcline, biotite and hornblende, 
and are set in a recrystallised amphibolite-like 
groundmass of those minerals, among which green 
hornblende is the most conspicuous. 

(Kirchspiel, Lavia, Finland.) 
E. Makinen : Geol. For. i Stockholm Fork., xxxvii, 1915, 

p. 388. 

Ledntiorite, Shand, 1910. An altered melanite-augite- 
nepheline-syenite associated with borolanite, but 
free from the pseudo-porphyritic character of the 
latter. (Ledmore River, Assynt.) 

S. T. Shand : Trans. Edin. Geol. Soc., ix, 1910, p. 384. 
Leeuwfonteinite, Molengraaff, 1904. - - A variety of 
alkali-syenite containing barkevikite, and charac- 
terised by an abundance of anorthoclase. Por- 
phyritic varieties also occur. 

(Leeuwfontein, Bushveld.) 
H. A. Brouwer : Journ. Geol., xxv, 1917, p. 775. 

Leidleite, Thomas & Bailey, 1915. A porphyritic 
rock containing phenocrysts of plagioclase (labra- 
dorite to anorthite) in a subviarolitic groundmass 
of felspar, augite, and glass. (Glen Leidle, Mull.) 
E. M. Anderson & E. G. Radley : Q.J.G.S., Ixxi, 1915, p. 

Lemberg's Reaction. A test for the discrimination of 
calcite and dolomite. Lemberg's Solution, log- 
wood digested in an aqueous solution of aluminium 


chloride, is used as a combined stain and reagent. 
Calcite (and aragonite) are stained violet after 
treatment for about ten minutes, while dolomite 
' remains unchanged. 

Lenne Porphyry, v. Dechen. A group name for the 
keratophyres and associated crystal-tuffs of the 
Lenne Valley, Westphalia. 

Leopardite, Hunter, 1853. A variety of quartz- 
porphyry containing small phenocrysts of quartz 
in a microgranitic or microgranophyric ground- 
mass of quartz, orthoclase, albite, and mica. The 
rock has a characteristically spotted or streaked 
appearance due to staining by hydroxides of iron 
and manganese. 
T. L. Watson : Journ. Geol., xii, 1904, p. 215. 

Lepidoblastic, Becke, 1903. A metamorphic texture 
due to the development during recrystallisation of 
minerals such as micas and chlorite having a flaky 
or scaly habit. 

Leptite, Hummel, 1870. A term, used especially by 
Swedish and Finnish geologists, applied to fine- 
grained granular metamorphic rocks composed 
mainly of quartz and felspar with subordinate mafic 
minerals ; = Granulite, = Halle flint gneiss. 
A. G. Hogbom : Bull. Geol. Inst. U-psala, x, 1910, p. 42. 
P. Eskola : Bull. Comm. Geol. F inlands, No. 40, 1914, p. 131. 

Leptynite, Hauy, 1822. A term applied to felspathic 
granulites which differ from halleflintas in having 
a coarser grain. 

Lcptynolite, Cordier, 1868. A fissile or schistose 
variety of hornfels containing mica, quartz and fel- 
spar, with or without minerals such as andalusite 
and cordierite. Cf. Cornubianite. 
A. Lacroix : Bull. Serv. Carte Geol. France, x, 1898, -p. 8. 
J. S. Flett : Mem. Geol. Surv. (Padstow and Camelford), 
1910, p. 72. 

Lestiwarite, Brogger f 1898. A leucocratic micro- 
syenite or syenite-aplite. (Lestiware, Finland.) 
W. C. Brogger : Eru-ptivgest. Kristiania, iii, 1898, p. 209. 



Leucite-basalt, Zirkel, 1870. A basaltic rock essen- 
tially composed of leucite, pyroxene and olivine. 

Leucite-phonolite. According to Rosenbusch this is 
a volcanic rock whose felsic minerals are leucite 
and orthoclase, without nepheline. With the ad- 
dition of nepheline (or nosean, etc.) the rock be- 
comes a leucitophyre. It is preferable, however, 
to follow Zirkel, who calls the latter leucite-phono- 
lite, and the former, from which nepheline is ab- 
sent, leucite-trachyte. 

Leucite Rocks. (References) 

W. Cross: Am. Journ. Sci., iv, 1897, p. 115. 

H. S. Washington: Carnegie Inst. Wash. Pub., 57, 1906; 

Journ. Geol., xv, 1907, p. 257. 
J. P. Iddings & E. W. Morley : Journ. Geol., xxiii, 1915, 

p. 231. 
A. Lacroix : C.R., clxvi, 1917, p. 486. 

Leucite-Syenite. A felspathoidal syenite containing 
leucite, or, more generally, pseudo-leucite, the 
latter consisting mainly of orthoclase and 
A. Lacroix : C.R., clxv, 1917, p. 1032. 

Leucite-tephrite. -- A variety of tephrite containing 
both leucite and nepheline, or nosean, etc. Cf. 

Leucite-trachyte, ^. Rath. A volcanic rock contain- 
ing leucite in addition to the constituents of 
tracrlyte = leucit e phonolite of Rosenbusch. 

Leucitite. A fine-grained or porphyritic rock, com- 
posed essentially of leucite and pyroxene ; a 
basaltic rock with leucite instead of plagioclase, 
and free from olivine. 

Leucitophyre, Coquand, 1857. A variety of leucite- 
phonolite, containing leucite and nepheline, or 
other soda felspathoid, with generally inconspicu- 
ous felspar ; the characteristic mafic constituent is 
segirine or aegirine-augite. 

Leuco-. A prefix added to the names of rocks to in- 
dicate a leucocratic character. Cf. Melano-. 


LeuCOCratic, Brogger, 1894. A term applied to facies 
of igneous rocks, or to members of a series of asso- 
ciated rocks, which are abnormally poor in mafic 
(dark and heavy) minerals relative to the normal or 
average rock-type of the mass or series. 

LeilCOphyre, Gilmbel. A variety of diabase contain- 
ing saussuritised felspar, pale green and purple 
pyroxenes, ilmenite and abundant chlorite. 

LeUCOtephrite, Fouque & Michel-Levy, 1879. A 
term for tephrites containing leucite, but free from 
nepheline or other soda felspathoid. The form 
leucitephrile is preferable, as leucotephrite sug- 
gests a leucocratic tephrite. 

Lherzite, Lacroix, 1917. -- A holomelanocratic rock 
composed of brown hornblende and biotite, with a 
little ilmenite and occasionally garnet. The 
chemical composition indicates that it contains 
potential nepheline and leucite, and that it is a 
heteromorphic form of theralite. 

(Lherz, Pyrenees.) 
A. Lacroix : C.R., clxv, 1917, p. 385. 

Lherzolite, De la Metherie, 1797. A variety of peri- 
do>tite containing both monoclinic and ortho- 
rhombic pyroxenes in addition to olivine. 

, (Lherz, Pyrenees.) 

A. Lacroix : Nouv. Arch, du Mus. <THist. Nat., 3 Ser., vi, 
p. 209. 

Liebenerite-porphyry. An altered nepheline-porphyry 
in which the phenocrysts of nepheline have been 
replaced by a scaly sericitic aggregate. 

(Predazzo, Tyrol.) 

Lignite. A general term applied to coal-like deposits 
usually of post-Carboniferous age, the most recent 
approaching peat and the oldest approximating 
to bituminous coal. Lignite is distinguished from 
brown coal by containing over 20 per cent, of 
water, and from ordinary coal by the fact that an 


aqueous solution of potassium hydroxide is without 
effect on the latter, whereas it dissolves lignite in 
part, giving a brown solution. 

Mem. GeoL Surv. Spec. Rep., Mineral Resources of Great 

Britain, vii, 1918. 

Limburgite, Rosenbusch, 1872. A rock consisting of 
phenocrysts of olivine and pyroxene in an alkali- 
rich glassy base ; = Magma-basalt, = (chemically) 
Nepheline-basalt (with glass in place of nepheline). 

(Limburg, Kaiserstuhl.) 

Lime-b9Stonite, Brogger, 1894. -- A variety of bos- 
tonite containing a notable amount of actual or 
normative anorthite in the plagioclase or pyroxene 

W. C. Brogger : Q.J.G.S., 1, 1894, p. 23. 

J. V. Elsden : Q.J.G.S., Ixi, 1905, p. 594. 

Limestone. - - A general term for bedded rocks of 
exogenetic origin, consisting predominantly of 
calcium carbonate. 

J. G. Goodchild : GeoL Mag., 1890, p. 71. 
E. W. Skeats : Bull. Mus. Com-p. Zool. Harvard, xlii, 1903, 

P- 53- 

E. Steidtmann : Journ. GeoL, xix, 1911, pp. 223, 392. 
J. E. Carne & L. J. Jones : GeoL Surv. N.S.W., Min. Res., 

No. 25. 

Limurite, Zirkel, 1879. A contact rock formed 
between granite and calcareous rocks, char- 
acterised by an abundance of axinite (over 50 per 
cent.), and also containing diopside, actinolite, 
zoisite, albite, quartz and pyrrhotite. 
A. Lacroix : C.R., cxv, 1892, p. 739. 

Lindoite, Brogger, 1894. A leucocratic variety of 
solvsbergite. (Lindo Is., Christiania.) 

W. C. Brogger : Eru-ptivgest. Kristiania, i, 1894, p. 133. 

Linear Foliation. A term applied to foliation which 
is due to the linear arrangement of lamellar and 
prismatic minerals such as biotite and hornblende. 
It is often associated with mullion or rodding struc- 
ture where the foliation is itself parallel to the dip 
and pitch of the parallel series of folds of which 


that structure is one of the outward expressions. 
Cf. Mullion Structure. 

Mem. Geol. Surv. (N.W. Highlands), 1907, pp. 97-8, 245-7, 
and PL xlix, Figs, i & 2. 

Linophyric, C.I.P.W., 1906. A term applied to 
porphyritic rocks in which the phenocrysts are 
arranged in lines or streaks. 

Lion's Haunch Basalt, Teatt, 1888. A variety of the 

Dunsapie type (q.v-) of the Scottish Carboniferous 
basalts, characterised by the presence of glass, and 
sometimes of biotite and analcite, in the ground- 

J. S. Flett : Mem. Geol. Surv. Scot. (Edinburgh), 1910, p. 

Li pa rite, Roth, 1861. A term synonymous with 
Rhyolite (q.v.). (Lipari Is.) 

Liquation. A process of differentiation in which two 
immiscible liquids separate from their common 
solution (e.g., from a magma). The term has also 
been applied to the separation of residual liquid 
from crystals already formed. 

N. L. Bowen : Journ. Wash. Acad. Sci. } viii, 1918, p. 88. 

F. F. Grout : Journ. Geol., xxvi, 1918, p. 657. 

Listwanite, Rose. - - A schistose rock of yellowish- 
green colour composed of various combinations of 
the minerals quartz, dolomite, magnesite, talc, 
an,d limonite. (Beresowsk, Urals.) 

Litchfieldite, Bayley, 1892. A nepheline-syenite con- 
taining albite and dark mica, and in some varieties 
having cancrinite in addition to nepheline ; inter- 
mediate in respect of its felspars between mariu- 
polite (albite) and foyaite (orthoclase). 

(Litchfield, Mass.) 

W. S. Bayley : Bull. Geol. Soc. Am., iii, 1892, p. 231. 
R. A. Daly : Bull. Geol. Soc. Am., 1918. 

LithlC Tuffs, Pirsson, 1915. Volcanic tuffs, in which 
the most conspicuous elements are fragments of 
rocks. Cf. crystal and vitric tuffs. 
L. V. Pirsson : Am. Journ. Sci., xl, 1915, p. 191. 


Lithoidal. A term meaning " stone-like" applied to 
compact aphanitic materials. 

Lithoidite, v. Rirtthofen, 1860. A rhyolite without 
phenocrysts, made up entirely of cryptocrystalline 
felsitic matter. 

Lithology. The study of rocks as based on the 
megascopic observation of hand-specimens. In 
its French usage the term is synonymous with 

Lithophysae, v. Rickthofen, 1860. A term applied to 
hollow spherulites, often radial and concentric in 
structure, occurring in rhyolite, obsidian and allied 

G. A. J. Cole : Q.J.G.S., xli, 1885, p. 162. 

F. E. Wright : Butt. Geol. Soc. Am., xxvi, 1915, p. 255. 

Lithosiderite, Brezina, 1885. A group name for 
stony-iron meteorites belonging to the sub-groups 
of siderophyre and pallasite. Cf. Siderolite. 

Lit-par-lit Injection. A term used to designate the 
intimate penetration of bedded, schistose or other 
fissile formations by innumerable narrow sheets 
and tongues of granitic magma = Leaf-by-leaf 
T. O. Bosworth : Q.J.G.S., Ixvi, 1910, p. 380. 

Load Metamorphism, Daly, 1911. A name for a 
type of static metamorphism in which high tem- 
perature has been a controlling influence, as well 
as overhead pressure. 
R. A. Daly : Bull. Geol. Soc. Am., 28, 1917, p. 400. 

Loam. A detrital deposit containing nearly equal 
proportions of sand, silt, and clay, these terms 
referring to the grade-sizes of the particles. The 
term has generally been used in a much wider 
sense, the restricted definition here given having 
emerged during recent years as a result of grading- 
work for economic purposes. 

Lode or Vein. General terms for epigenetic mineral 
deposits, the form of which is characterised by 


small thickness in relation to depth and length. 
In America the term vein is used in preference to 

Lodranite, Meunier, 1882. - - A siderolitic meteorite 
containing- crystals of olivine and bronzite in a 
matrix of nickel-iron. 

Loess. A widespread deposit of silt or marl extending 
from Central Europe through the steppes of Asia. 
It is a buff-coloured, porous, but coherent deposit 
traversed by a network of narrow tubes represent- 
ing the negatives of successive generations of 
grass-roots. The comminution of the constituents 
is ascribed to the grinding action of glaciers, the 
fine grade and distribution to the action of wind, 
and the accumulation in thick deposits to the grip 
of vegetation. 

Longulites, Vogelsang, 1870. Elongated crystallites 
of cylindrical or conical forms considered to be 
formed by the adhesion of linear series of globu- 
F. Rutley : Min. Mag., ix, 1891, p. 261. 

Lopolith, Gvout, 1918. -- A large lenticular intrusive 
body of igneous rock, generally concordant, and 
differing from a sill by being centrally depressed, 
so that its upper surface is basin-like. 

F. F. Grout : Am. Journ. Sci., xlvi, 1918, p. 516. 
Luciite, Chelius, 1892. A fine-grained variety of 

diorite, composed essentially of plagioclase, horn- 
blende, and in some varieties a little quartz. The 
type differs from malchite only in its coarser grain. 
Lugarite, Tyrrell, 1912. A porphyritic rock contain- 
ing phenocrysts of titanaugite and barkevikite, 
with small and variable amounts of labradorite, in 
a base of analcite (with traces of nepheline) which 
makes up about half of the rock. 

(Lugar, Ayrshire.) 

G. W. Tyrreli : Q.J.G.S., Ixxii, 1917, p. 107. 
Lujaurite, Brogger, iSgo-LujaVtite, Ramsay, 1894. 

A variety of nepheline-syenite, with trachytoid 


texture, containing aegirine, and characterised by 
the conspicuous presence of eudialyte. 

(Lujaur Urt, Kola.) 
W. Ramsay : Fennia, xv, 2, p. 3. 

Ltindyite, Hall, 1914. An intrusive rock with ortho- 
phyric texture characterised by a high percentage 
of alkalies and the presence of a catophorite-like 
amphibole. The rock has been, analysed, but not 
described. (Lundy Is.) 

Summ. Prog. GeoL Surv. (1914), 1915, pp. 53 & 56. 

LllSCladite, Lacroix, 1920 A type of olivine- 
theralite or essexite characterised by the general 
absence of hornblende (cf. Berondrite), and the pre- 
sence of olivine and often of biotite. Orthoclase 
mantles the plagioclase, and nepheline, not abun- 
dant, occurs interstitially. The Crawfordjohn 
essexite is a British example, and kylite is a 
melanocratic type. 

(Ravin de Lusclade, Mont-Dore.) 
A. Lacroix : C.R., clxx, 1920, p. 21. 

Lusitanite, Lacroix, 1916. A mesocratic alkali-syenite 
containing riebeckite and aegirine. 

(Alter Pedroso, Portugal.) 
A. Lacroix : C.R., clxiii, 1916, p. 279. 

Llixullianite, Pisani, 1864. A variety of tourmalinised 
granite, in which the tourmaline occurs as radiat- 
ing sheaves of acicular crystals embedded in 
quartz. (Luxulyan, Cornwall.) 

T. G. Bonney : Min. Mag., i, 1877, p. 215. 

J. S. Flett : Mem. Geol. Surv., 347 (Bodmin and St. Austell), 
1909, p. 66. 

Lydite. - - A siliceous rock of extremely fine grain, 
composed essentially of quartz and chalcedony ; 
usually grey-black, owing to carbonaceous matter ; 
but sometimes brown or green, due to the presence 
of iron hydroxides or chlorite respectively. Lydite 
occurs as chert-like bands in the older formations, 
where it represents silicified shales, limestones or 
tuffs. = Lydian Stone. 



Macedonite, Skeats & Summers, 1909. An aphanitic 

basaltic rock containing- minute felspars, nosean, 

melilite, perovskite, and pseudomorphs after 

olivine (serpentine or chlorite) in a green vitreous 

or chloride base. (Mt. Macedon, Victoria.) 

E. W. Skeats : Australian Ass. Ad. Sci. (1909), 1910, p. 173. 

Geol. Surv. Victoria, Bull. No. 24, 1912. 

Maculose, Holmes, 1919. A term suggested for a 
group of contact-metamorphosed rocks, including 
spotted " slates," knotenschiefer, and hornfels, to 
connote their spotted, knotted, and gnarled struc- 
tures. The term may be applied to either the rocks 
or their structures, and serves to distinguish them 
from those described as gneiss ose, granules e, and 
schistose, into any of which maculose rocks and 
structures may pass by the continued action of 
more intense metamorphism. See Table on p. 280. 

Madeirite, Gagel, 1912. - - A porphyritic variety of 
alkali-picrite containing abundant phenocrysts of 
titaniferous augite and somewhat serpentinised 
olivine in a groundmass consisting mainly of 
augite and magnetite with a little plagioclase. 
C. Gagel : Zeit. Deutsch. Geol. Ges.s., Ixiv, 1912, p. 399, and 
PI. vii. 

Madupite, Cross, 1897. A fine-grained rock, consist- 
ing essentially of phenocrysts of diopside and 
phlogopite in a ground mass of glass having 
approximately the composition of leucite. 
W. Cross : Am. Journ. Sci., iv, 1897, p. 139. 

Maenaite, Brogger, 1894. A fine-grained holocrystal- 
line rock intermediate in type between the mon- 
zonitic felsites and the dioritic lamprophyres, and 
characterised by an abundance of hornblende. 

(Maena, South Norway.) 

Mafic, C.I.P.W., 1912. A mnemonic term for the 
ferromagnesian and other non-felsic minerals 
actually present in an igneous rock, and also 

L applied to rocks in which those minerals pre- 


dominate ; not synonymous with femic, which 
refers to the normative constituents of a rock cal- 
culated from its chemical analysis. 
C.I.P.W. : Journ. Geol., xx, 1912, p. 561. 

Mafraite, Lacroix, 1920. A heteromorphic form of 
berondrite containing- soda-hornblende in large 
idiomorphic crystals, together with pyroxene and 
labradorite. The type differs from berondrite by 
the absence of nepheline, the constituents of that 
mineral being- present in the amphibole. 

(Mafra, Cintra, Portugal.) 

Magma. A comprehensive term for the molten fluids 
generated within the earth from which igneous 
rocks are considered to have been derived by 
crystallisation or other processes of consolidation. 
A magma includes not only the material repre- 
sented by all or part of an igneous rock, but also 
any volatile fluxes and residual liquors which may 
have escaped during or after consolidation. It is 
therefore not correct to assume that the composi- 
tion of a rock represents that of the magma from 
which it developed. In the case of suddenly 
chilled margins this may except for gases and 
vapours be nearly true, but where the rocks of 
an area reveal differentiation into a wide range of 
types, these types may represent chemically only 
fractions of the bulk-magma, and from the latter 
therefore they may differ very considerably. 

Magma-basalt, Boricky, 1872. A term in part synony- 
mous with Limburgite (q.v.), but also applied to 
porphyritic, glassy basaltic rocks more closely re- 
lated to ordinary basalt. 

Magmatic Assimilation. See Assimilation. 

Magmatic Stoping, Daly, 1906. A process whereby 
rock magmas are enabled to take the place pre- 
viously occupied by pre-existing rocks, involving 
(i) marginal shattering of the rocks along the roof 
and walls of the magmatic chamber ; and (2) sink- 


ing of the blocks and fragments so produced, with 
concomitant occupation of the space so liberated, 
by lateral or upward movement of the magma. 
R. A. Daly : Ig. Rocks and their Origin, New York, 1914, 
P- 194. 

Magnesian Limestone. In its petrological usage (as 
opposed to its stratigraphical application to a Per- 
mian formation) this term has been given to lime- 
stones containing MgCO 3 (about 5 to 15 per cent.), 
but in which dolomite cannot be detected either 
optically, or by the Lemberg reaction. Such 
rocks are thus distinguished from Dolomitic Lime- 
stone, in which dolomite is demonstrably present 
in addition to calcite. The connotation of mag- 
nesian limestone is, however, generally interpreted 
more widely, especially as a field-term. 
R. C. Wallace : Cong. Geol. Inter,, C.R. xii (1913), 1914, 

P- ^75. 
D. \Voolacott : Geol. Mag., 1919, pp. 452 and 485. 

Magnesite Rock. A carbonate rock consisting pre- 
dominantly of the mineral magnesite. 

T. Crook : Trans. Ceramic Soc., 1919, p. 67. 

Magnetite-hogbomitite, Gavelin, 1917. A rock com- 
posed of numerous crystals of grey hogbomite, and 
occasional flakes of white hydrargillite, in a black 
magnetite-ilmenite matrix. Hogbomite is a 
mineral having the composition RO.2R 2 O 3 where 
RO is mainly MgO, and R 2 O 3 is mainly A1 2 O 3 and 
Fe 2 O 3 , together with a certain amount of TiO 2 . 
A. Gavelin : Bull. Geol. Inst. U-psala, xv, 1917, p. 310. 

Magnetite-olivinite, Sjogren, 1876. A variety of 
dunite rich in titaniferous magnetite and contain- 
ing shreds of biotite. (Taberg, Sweden.) 

Magnophyric, C.I.P.W., 1906. A term applied to 
coarsely porphyritic rocks with phenocrysts ex- 
ceeding 5 mm. in one or more of their dimensions. 

Malchite, Osann, 1892. A term applied to rocks 
which have been described asi micro-diorite, or 


diorite-felsite, and which differ from porphyrite by 
the absence of conspicuous phenocrysts. 


Mem. Geol. Surf. Scotland (Glen Coe), 1916, pp. 156, 175. 

Malignite, Laws on, 1896.- A melanocratic variety of 
nepheline-syenite. (Maligne R., California.) 

A. C. Lawpon : Bull. De-pt. Geol. Univ. California, Pub. i, 
1896, p. 337. 

R. A. Daly : Bull. Geol. Soc. Am., 1906, xvii, p. 329. 

Manganolite, Wadsworth, 1891. A general term pro- 
posed for rocks composed of manganese-minerals. 

Mangerite, Kolderup, 1903. A variety of monzonite. 

(Manger, near Bergen.) 
C. F. Kolderup : Bergen Mus. Aarbeit., No. 12, 1903, p. 107. 

Manjak. A black variety of bitumen, having a bril- 
liant lustre and conchoidal fracture; H about 2; 
S.G. = 1.06-1.07. (Barbados.) 

Marble. A general term for any calcareous or other 
rock of similar hardness that can be polished for 
decorative purposes ; petrologically restricted to 
granular crystalline limestones, the term, when 
used without a mineralogical prefix, implies a 
variety such as statuary marble, composed almost 
entirely of calcite. 

Marekanite. A variety of perlitic rhyolite-glass from 
which large perlitic masses of clear glass readily 
separate. (Marekana, Okhotsk, Siberia.) 

J. W. Judd : Geol. Mag., 1886, p. 241. 

K. Bogdanovitch : Fundort des Marekanits, St. Petersbourg, 

Mareugite, Lacroix, 1917. An even-grained theralitic 

rock, consisting of bytownite and hauyne with 

variable and sometimes considerable amounts of 

hornblende and augite. (Mareuge, Auvergne.) 

A. Lacroix : C.R., clxiv, 1917, p. 587. 

Margarite, Vogelsang, 1872. An aggregate of globu- 
lites, or minute sphere-like crystallites, arranged 
like beads in a linear series. 
F. Rutley : Min. Mag., ix, 1891, p. 261. 


Margination Texture, Plolmquist, 1906. A texture 

due to magmatic corrosion phenomena in granites ; 
characterised by curved and sinuous contacts be- 
tween quartz and felspar, the material of later 
crystallisation having corroded the mineral already 
P. J. Holmquist : Bull. Geol. Inst. U-psala, vii, 1906, p. 116. 

Mariupolite, Morozewicz, 1902. An albite-nepheline- 
syenite of variable grain, containing segirine and 
lepedomelane, with zircon and beckelite as notable 
accessories. (Mariupol, Sea of Azov.) 

Markfieldite, Hatch, 1909. --An igneous rock com- 
posed of idiomorphic crystals of plagioclase, to- 
gether with augite and/ or hornblende, embedded 
in a gro'undmass of micropegmatite. The term 
thus denotes a dioritic granophyre, intermediate 
between granophyre and granodolerite. 

(Markfield, Charnwood Forest.) 

Markle Basalt, Hatch, 1892. A type of the Scottish 
Carboniferous basalts ; characterised by the pre- 
sence of large and numerous phenocrysts of labra- 
dorite with small grains of olivine in a normal 
basaltic groundmass. The type differs from the 
Jedburgh type in being much more conspicuously 

E. B. Bailey : Mem. Geol. Surv. Scot. (East Lothian), 1910, 
p. 120. 

G. W. Tyrrell : Trans. Geol. Soc. Glasgow t xiv, 1912, p. 241. 

Marl. A general term for calcareous clay or calcare- 
ous loam. 

Marloesite, Thomas, 1911. A rock somewhat re- 
sembling pantellerite, containing glomero-por- 
phyritic groups of olivine and albite-oligoclase in a 
felted! ground mass composed largely of soda- 
felspar. (Marloes, Skomer Is., Pembroke.) 
H. H. Thomas : Q.J.G.S., Ixvii, 1911, p. 175. 


Marosite, Iddings, 1913. A variety of shonkinite con- 
taining- augite and biotite, with subordinate alkali- 
felspar and felspathoid. (Pic de Maros, Celebes.) 
J. P. Iddings & E. W. Morley : Journ. Geol., xxiii, 1915, p. 

Marscoite, Harker, 1904. A hybrid rock, due to the 
partial absorption of granitic material by a gabbro 
magma, containing xenocrysts of quartz and 
felspar in a gabbroid matrix of abnormal composi- 
tion. The name is intended for local use only, and 
not to connote a new rock-type. (Marsco, Skye.) 

A. Harker : Mem. Geol. Surv. (Tert. Ig. Rocks, Skye), 1904, 
pp. 175, 186. 

Masanite, Koto, 1909. A variety of quartz-monzonite- 
porphyry having phenocrysts of zoned plagioclase 
and corroded quartz in a finely granitic or micro- 
pegmatitic groundmass. (Ma-san-po, Korea.) 

Masanophyre, Koto, 1909. A variety of masanite in 
which the felspar phenocrysts consist of oligoclase 
mantled with orthoclase, and of which the ground- 
mass contains blue-green hornblende, and sphene. 

B. Koto : Journ. Col. Sci., Tokyo, xxvi, 1909, p. 189. 

Mediophyric, C.I.P.W., 1906. -- A term applied to 
porphyritic rocks with phenocrysts between 5 mm. 
and i mm. in their longest dimensions. 

Mediosilicic, Clarke, 1911. A term suggested in place 
of "intermediate" to connote that the rocks so 
described have a silica-content falling between 52 
and 66 per cent. 

Megascopic. A general term, more appropriate than 
macroscopic, applied to observations made on 
minerals and rocks, and to the characters 
observed, by means of the naked eye or pocket- 
lens, but not with a microscope. 

Meigen's Reaction. A test for the discrimination of 
calcite and aragonite. A solution of cobalt nitrate 
is used as a combined stain and reagent. 
Aragonite is stained to a lilac tint which remains 
visible in thin section, after boiling with the solu- 


tion for about twenty minutes ; calcite (and dolo- 
mite) may be stained pale blue, but appear un- 
changed in thin section. 

Melanocratic, Brogger, 1894. - - A term applied to 
rocks, or to members of a series of associated 
rocks, which are abnormally rich in mafic (dark 
and heavy) minerals relative to the normal or 
average* rock-type of the mass or series. 

Melano-, Mela-. Prefixes added to the names of rocks 
to indicate a melanocratic character. Cf. Leuco-. 

Melaphyre, Brohgniairt, 1813. A general term for 
altered and amygdaloidal rocks of basaltic or 
andesitic types. 

B. von Cotta : Rocks Classified and Described, trans, by P. 
H. Lawrence, 1878, p. 154. 

Melilite-basalt, v. Rath, 1866. A highly under- 
saturated basaltic rock essentially containing 
augite, melilite, and olivine. Nepheline is fre- 
quently present, and perovskite and spinellids are 
characteristic accessories. 

A. VV. Rogers & A. L. Du Toit : Trans. S. Af. Phil. Soc., 
xv, 1904, p. 61. 

G. T. Prior : Min. Mag., 1903, p. 228. 

Melilitite, Lacroix, 1896. An igneous rock essentially 
composed of melilite and pyroxene. Nepheline- 
and leucite-melilitites are distinguished ; and by the 
introduction of olivine the rocks become meliHte- 
basalts. When the felspathoid minerals are 
dominant the terms melilite-nephelinite , or -leucitite 
may be used ; and when olivine is also present, 
melilite-nepheline-basalt, or -leucite-basalt.. 
A. Lacroix : Min. de la France, ii, 1896, p. 501. 

Merocrystalline. = Hemicrystalline. 

MeSO-, Grubenmann, 1907. A prefix used as a quali- 
fier to the group-names suggested by Grubenmann 
for metamorphic rocks, to indicate that the type so 
distinguished belongs to the " middle zone " of 
metamorphism. In this zone the distinctive 


physical conditions are high temperature and 
hydrostatic pressure and intense stress, and the 
rocks characteristically produced include mica- 
schists, garnetiferous and staurolite-schists, horn- 
blende-schists, amphibolite and various types of 
crystalline limestones, quartzites and gneisses. 
Cf. Epi-, and Kata-. 
U. Grubenmann : Die Kristallinen Schiefer, II, 1907, pp. 

21, 172. 

MeSOCratic. - - A term applied to facies of igneous 
rocks, or to members of a series of associated 
rocks, which are somewhat richer in mafic (dark 
and heavy) minerals than the normal or average 
rock-type of the mass or series, but not suffi- 
ciently rich to be called melanocratic. 

MeSOSiderite, Rose, 1864. A general terrn^ for 
achondritic meteorites in which both silicate- 
minerals and nickel-iron are present in large pro- 
portions ; = Siderolite. 

MeSOStasis. A term applied to the ultimate inter- 
stitial material of a rock which consolidated in the 
final stage of solidification as a glass (e.g., in in- 
tersertal basalts), a single mineral (e.g., analcite, 
in teschenite), or a eutectic (e.g., micropegmatite, 
in granodolerite). 

Meta-. A prefix used before the names of igneous 
rocks to signify that the mineral and chemical com- 
position of the latter have been modified by altera- 

Metabasite, Hackman, 1907. A general term for 
metamorphosed basaltic, doleritic and allied rocks, 
the types included ranging from diabase and 
epidiorite to hornblende-schist. 

J. J. Sederholm : Bull. Comm. Geol. Finlande, No. 23, 1907, 
p. 92. 

Metabolite, Wadsworth, 1891. A term proposed for 
altered trachyte-glass, the fresh rock being 
described as lassenite. 



Metacrystal, Lane, 1902. A term applied to the large, 
pseudoporphyritic crystals, such as staurolite and 
garnet, in metamorphic rocks ; == Porphyroblast. 
A. C. Lane : Bull. Geol. Soc. Am., xiv, 1902, p. 386. 

Metallogeny. - - The genetic study of ore-deposits in 
relation to age, regional tectonics, and petro- 
graphic provinces. Metallogenic provinces and 
epochs are recognised. 

A. M. Finlayson : Q.J.G.S., Ixvi, 1910, p. 281. 

C. Iwaski : Journ. Col. Sci. Tokyo, xxxii, 1912, No. 8. 

W. G. Miller & C. W. Knight : Trans. Roy. Soc. Canada, 
ix, 1915, p. 241. 

L. L. Fermor : Proc. Asiatic Soc. Bengal, xv, 1919, p. clxx. 

Metamorphic Differentiation, Stillwell, 1918. -- The 
segregation into definite minerals of materials which 
has migrated from other parts of the rocks con- 
cerned by metamorphic diffusion (see below). 
F. L. Stillwell : Aust. Ant. ' Ex$ed. Sci. Re-p. A, iii, 
i (i) (Met. Rocks, Adelie Land), 1918, p. 72. 

Metamorphic Diffusion, Stillwell, 1918. The migra- 
tion by diffusion of material from one part of a 
rock to another during its recrystallisation. 

F. L. Stillwell : Aust. Ant. Escaped. Sci. Rep. A, iii, 
i (i) igiS, (Adelie Land and critical discussion). 

Metamorphic Rocks. Rocks derived from pre-exist- 
ing rocks by mineralogical, chemical, and 
structural alterations due to endogenetic pro- 
cesses ; the alteration having been sufficiently 
complete throughout the body of the rock to have 
produced a well-defined new type. (For references 
see below, p. 156.) 

Metamorphism, Lyell, 1833. The sum of the thermo- 
dynamic processes of endogenetic origin which 
cause the transformation of a rock into a well 
characterised new type by more or less thorough 
recrystallisation, and change of texture and 
structure, with or without the introduction of new 
material. By some authors (Van Rise, Leith & 
Mead, et alitcr) metamorphism is defined so as to 


include all the changes in rocks after their crystal- 
lisation from magmas. This extreme overburden- 
ing of the term makes it synonymous with altera- 
tion, and thereby renders it useless. Disregard- 
ing the etymology of the word, it is expedient to 
restrict its significance to endogenetic alterations 
as denned above. A full account of the varied 
usage is to be found in the paper by Daly referred 
to below. 

G. Barrow : Q.J.G.S., xlix, 1893, p. 330. 

F. Becke : Cong. Geol. Inter., C.R. ix. 1903, p. 553 (Mine- 
rals and Structures). 

C. R. Van Hise : U.S.G.S., Mon., 47, 1904 (General). 

Mem. Geol. Surv. (N.W. Highlands), 1907. 

E. S. Bastin : Journ. Geol., xvii, 1909, p. 449; and xi, 1913, 
p. 193 (Criteria of origin). 

U. Grubenmann : Die Kristallincn Schiefer, Berlin, 1910. 

V. M. Goldschmidt : Die Kontactmetamor-pJwse im Kris- 
tiania-gebiet, 1911. 

Mem. Geol. Surv., 359 (Lizard), 1912. 

J. D. Truemann : Journ. Geol., xx, 1912, p. 236 (Criteria of 

L. Milch : Journ. Geol., xx, 1912, p. 272. 

J. Johnston & P. Niggli : Journ. Geol. xxi, 1913, p. 610 

C. K. Leith & W. J. Mead : Metamor-phic Geology, 1915. 

R. A. Daly : Bull. Geol. Soc. Am., xxviii, 1917, p. 375 
(Classifications and Definitions). 

A. Harker : Q.J .G.S., Ixxiv, 1918, p. Ixiii (General review). 

J. J. H. Teall : Proc. Geol. Assoc., xxix, 1918, p. i (Dyna- 

W. Lindgren : Journ. Geol., xxvi, 1918, p. 542 (Volume 

F. L. Stillwell : Aust. Antarc. Ex-ped. Set. Re-p., Vol. A, 
iii, i (T) 1918, (Adelie Land and critical discussion). 

T. G. Bonney : Geol. Mag., 1919, pp. 196, 246 (Foliation). 

Metasomatism, Naumann. - - The processes by which 
one mineral is replaced by another of different 
chemical composition owing to reactions set up by 
the introduction of material from external sources. 
Metasomatic rocks are those whose chemical com- 
position has been substantially changed by the 
metasomatic alteration of its original constituents. 
W. Lindgren : Econ. Geol., vii, 1912, p. 521 ; Journ Geol., 
xxvi, 1918, p. 543. 


Metastable, Os timid t 1897. - - A term describing- the 
condition of a supersaturated solution in which the 
presence of the .solid phase is necessary to stimu- 
late the separation of the solute. 

H. A. Miers : Trans. Chem. Soc., Ixxxix, 1906, p. 427. 

Meteorite. A general term for mineral aggregates of 
cosmic origin that reach the earth by falling 
through the atmosphere from interplanetary space. 

O. C. Farringdon : Journ. Geol., ix, 1911, p. 51, etc. 

G. T. Prior : Min. Mag., xviii, 1916, p. 26. 

Miaskite, Rose, 1839. A variety of nepheline-syenite 
containing biotite as the chief mafic constituent. 
, (Miask, Urals.) 

Mica-Schist. A schist composed essentially of micas 
and quartz, the foliation being mainly due to the 
parallel disposition of the mica-flakes. Quartz 
may be granular or lenticular. Many varieties are 
recognised, such as those containing garnet or 
staurolite, in addition to the group minerals, and 
are distinguished by the use of prefixes specifying 
the chief varietal mineral. 

Micro-. A prefix commonly added (i) to the names 
of megascopic textures to indicate a texture of 
similar type developed on a microscopic scale ; 

e.^., microgranitic, micrographic, micro- 

Doikilitic, etc. ; (2) to the names of phanerocrystal- 
line rocks to indicate a microcrystalline rock or 
groundmass of corresponding mineral composi- 
tion and texture; e.g., microgranite, micro- 
diorite, microsyenite, etc. 

Microcrystalline. A term applied to a rock or ground- 
mass in which the individual crystals can only be 
seen as such under the microscope. 

Micrplites. -- A general term for minute crystals of 
tabular or prismatic habit, occurring in micro- 
crystalline or hemicrystalline rocks and ground- 
masses. Microlites are distinguished from crystal- 
lites by their capacity to give a reaction with 
polarised light. 


Microlitic Texture, Fouque & Michel Levy. The tex- 
ture of a porphyritic rock having a microcrystal- 
line groundmass composed largely of more or less 
idiomorphic tabular or prismatic crystals (e.g. , 
felspar laths) with or without interstitial glass. 
Micropegmatite, Michel Levy, 1896. - - A term for 
micrographic aggregates of quartz and felspar 
occurring as a gro mdmass or mesostasis in vari- 
ous igneous rocks. 

T. H. Holland : Q.J.G.S., liii, 1897, p. 405. 
W. Mackie : Trans. Edin. Geol. Soc., ix, 1909, p. 247. 
S. J. Schofield : Geol. Surv. Canada Mus. Bull., 2 (Geol. 

Series No. 13), 1914. 
N. L. Bowen : Journ. Geol. Su-p-p. Vol., xxiii, 1915, p. 17. 

Microtinite, Lacroix 1901. A coarse-grained leuco- 
cratic rock of monzonitic or dioritic texture con- 
taining vitreous plagioclase (microtinite). The 
type occurs as enclaves homceogenes in lavas. 

(Roc Blanc, Auvergne.) 
A. Lacroix : C.R., cxxxi, 1900, p. 348. 

Migmatite, Sederholm, 1907. A term applied to com- 
posite rocks, such as gneisses, produced by the 
injection of granitic magma between the folise of 
a schistose formation. Cf. Composite gneiss. 
J. J. Sederholm : Bull. Comm. Geol. Finlande, 23, 1907, p. 


Miharaite, Tsuboi, 1918. A variety of basalt char- 
acterised by abundant phenocrvsts of bytownite 
and fewer of pyroxenes in an intersertal ground- 
mass containing occult free silica ; = bytownite- 
tholeiite. Cf. Cumbraite. 

(Mihara-yama, Japan.) 
Seitaro Tsuboi : Jonrn. Geol. Soc., Tokyo, xxv, 1918, p. 47. 

Mijakite, Peter sen ^ 1891. -- A red-brown porphyritic 
variety of basalt, containing phenocrysts of bvtow- 
nite and augite in a groundmass containing 
plagfioclase, magnetite, manganese-pyroxene and 
glass. (Mijakeshima, Japan.) 

Miliolite, Carter, 1849. A fine-grained limestone of 
?eolian origin occurring in Kathiawar, and con- 


sisting of the tests of Miliolina and other foramini- 
fera, oolitic grains, and mineral fragments, 
cemented by calcite. 

J. W. Evans : Q.J.G.S., Ivi, 1900, p. 559. 

Mimosite, Cordier, 1868. - - A melanocratic dolerite 

rich in augite and ilmenite. Cf. Soggendalite. 
Mineralisers. -- A term applied to magmatic gases, 
such as hydrogen, water and compounds ol 
fluorine, boron, sulphur, carbon, etc., and other 
volatile substances, which 

(i) by lowering viscosity, extending the tem- 
perature range of crystallisation, and acting as 
catalytic agents, are able to facilitate the crystal- 
lisation of various minerals ; (2) enter into the 
composition of certain minerals which could not 
otherwise be formed ; and (3) are capable of ex- 
tracting and concentrating metallic and other 
compounds from the magma through which they 
were originally dispersed. = Agents mineralisa- 

A. Marker : Nat. Hist. Ig. Rocks, 1909, p. 282. 
W. H. Goodchild : Mining Mag., xviii, 1917, p. 190; xix, 
1918, p. 189. 

Minette, Voltz, 1822. A syenitic lamprophyre com- 
posed essentially of biotite and orthoclase. The 
term was originally and still is> applied to the Jur- 
assic ironstones of the Briey basin and Lorraine. 

Minette-felsite, Bonney & Haughton, 1879. A term 
proposed for minette-like rocks having a micro- or 
crypto-crystalline groundmass : minette proper 
having a finely phanerocrystalline groundmass. 
T. G. Bonney : Q.J.G.S., xxxv, 1879, p. 166. 

Minophyric, C.I.P.W., 1906. - - A term applied to 
porphyritic rocks with phenocrysts between 
i mm. and 0.2 mm. in their longest dimensions; 
"phenocrysts " smaller than these are microlites. 

" Minus " Minerals, Lcewinson - Lessing, 1897. - 
Minerals (such as garnets) whose molecular 
volumes are less than the sum of the molecular 


volumes of the constituent oxides. In the case of 
allotropic modifications of the latter, the more con- 
densed form, having the smaller molecular volume, 
is assumed for the calculation. 

F. Loewirjson-Lessing : Cong. Geol. Inter., C.R. vii, 1897, 
p. 194. 

W. H. Goodchild : Mining Mag., xviii, 1917, pp. 243, 298. 

Minverite, Dewey, 1910. A proterobase, containing 
primary brown hornblende, purple-brown augite 
and albitised felspars; the type differs from albitc- 
diabase in the possession of primary hornblende. 

(St. Minver, N. Cornwall.) 
H. Dewey & J. S. Flett : Geol. Mag., 1911, p. 207. 
Mem. Geol. Surv., 335-6 (Padstow), 1910, p. 46. 

MisSOUrite, Weed & Pirsson, 1896. A phanero- 
crystalline rock, containing pyroxene, leucite, and 
olivine, and consequently the plutonic equivalent of 
a leucite-basalt. (Missouri.) 

W. H. Weed & L. V. Pirsson : Am. Journ. Sci., ii, 1896, 
P- 3*5- 

Mix-Crystal. A general term for crystals composed of 
two or more isomorphous or partly isomorphous 
constituents; e.g., felspars (NaAlSi,O a 
and CaAl 2 Si 2 O 8 ), hypersthene (MgSiO 3 and 
FeSiO 3 ), etc. 

Mode, C.I.P.W., 1902. The actual mineral composi- 
tion of a rock expressed quantitatively in percent- 
ages by weight, as opposed to the norm (q.v.). 

Moldavites. A term for the green obsidianites which 

occur as rolled pebbles in certain of the valleys of 

Bohemia. Their origin is obscure, but is almost 

certainly extra-terrestrial. (Moldau, Bohemia.) 

F. E. Wright : Bull. Geol. Soc. Am:, xxvi, 1915, p. 280. 

Molecular Proportion. The figure obtained for any 
constituent of a rock or mineral by dividing its 
percentage by its molecular weight. The alter- 
native term Molecular Number proposed by 
Washington is already applied to the sum of the 
atomic numbers of the atoms in a molecule of any 


compound, and is therefore not suitable for the 

purpose intended by Washington. For tables of 

molecular proportions see 
C.I.P.W. : Quantitative Classification of Igneous Rocks, 


H. S. Washington : U.S.G.S. Prof. Pa-p., 1917. 
J. F. Kemp : Handbook of Rocks, 1918, p. 171 et seq. 
A. Holmes : Petro graphic Methods and Calculations, 1920. 

Molecular Volume. The figure obtained by dividing 
the molecular weight of any substance by its 
specific gravity ; = Solid specific volume. 
W. H. Goodchild : Mining Mag., xviii, 1917, pp. 243, 298; 
xix, 1918, p. 84. 

Monchiquite, Rosenbusch &* Hunter, 1890. -- A 
melanocratic dyke rock, microcrystalline or 
porphyritic, containing abundant mafic minerals, 
with little or. no felspar, in an isotropic base, 
which consists, or has the composition, of anal- 
cite. Most examples contain olivine, and nep- 
heline- and leucite-bearing varieties are recognised. 
(Serra de Monchique, Portugal.) 

J. W. Evans : Q.J.G.S., Ivii, 1901, p. 38. 

Mem. Geol. Surv. Scot. (East Lothian), 1910, p. 107. 

A. Holmes : Geol. Mag., 1915, p. 324. 

Mondhaldeite, Graeff, 1900. A dyke rock of mon- 
zonitic composition containing phenocrysts of 
augite, hornblende, bytownite and leucite in a 
glassy base. (Mondhalde, Kaiserstuhl, Baden.) 

Monmouthite, Adams, 1904. -- A phanerocrystalline 
rock composed essentially of nepheline (about 70 
per cent.) and hornblende (hastingsite) with acces- 
sory albite, cancrinite and calcite. 

(Mon mouth Co., Ontario.) 

F. D. Adams : Am. Journ. Sci., xvii, 1904, p. 269. 

Monotropic. A term applied to the transition from 
one polymorphic form of a substance to another 
(e.g., MgSiO 3 as amphibole -> MgSiO 3 as mono- 
clinic pyroxene) when the change can take place 
only in one direction. It is possible, however, 


that monotropic processes may be so limited only 
when the action of shearing- stress is left out of 

Moiltrealite, Adams, 1913. -- A highly melanocratic 

variety of olivine-essexite. (Montreal.) 

F. D. Adams : Cong. Geol. Inter., C.R. xii, Guide, 3, 1913, 

P- 39- 

Monzonite, de Lapparent, 1864. A phanerocrystal- 
line rock, having approximately equal quantities 
of orthoclase and plagioclase, so that the rock is 
intermediate between syenite and diorite, or 
syenite and gabbro. It is desirable that the 
plagioclase should be at least as calcic as labra- 
dorite, and that rocks intermediate between syenite 
and diorite should be distinguished as syenodiorite, 
monzodiorite or orthoclase-diorite. 

(Monzoni, Tyrol.) 

W. C. Brogger : Ern-ptivgest. Kristiania, ii, 1895, p. 6. 
Monzonitic Texture. A texture characterised by the 
idiomorphism of plagioclase crystals with ortho- 
clase occupying part of the interstitial spaces. 
Mortar Structure. A mechanical structure in which 
small grains produced by granulation occupy the 
cracks or interstices between larger individuals. 
Mosaic Texture. A granulose texture of meta- 
morphic rocks in which the individual grains meet 
with nearly straight or but slightly curved con- 
tacts ; = Gran oblas tic. 

Mud Cracks. A general term for the irregular desic- 
cation fractures, crudely simulating a series of 
polygons, formed in the superficial layers of a 
deposit of mud exposed to the atmosphere. 
E. M. Kindle : 'fourn. Geol., xxv, 1917, p. 135. 
Mudstone. An indurated non-laminated sediment 
composed of clay-minerals and other constituents 
of the mud grade. Cf. Shale. 

Mugearite, Harker, 1904. -- A dark finely-crystalline 
rock of trachytic to loasaltic aspect, distinguished 
from basalt by the occurrence of oligoclase and 
orthoclase in place of labradorite, by generally con- 


taining- olivine in greater amount than augite, and 
by the possession of a trachytic rather than a 
basaltic texture. (Mugeary, Skye.) 

A. Harker : Mem. Geol. Surv. (Tert. Ig. Rocks, Skye), 1904, 
p. 265. 

J. S. Flett : Summ. Prog. Geol. Surv. for 1907, 1908, p. 119. 

Mullion Structure, Kinahan, 1891. A structure first 
observed in the folded metamorphic rocks of 
Donegal, recalling the appearance of the clustered 
columns which support the arches, or divide the 
lights of mullioned windows, in Gothic churches. 
The structure is also described as Rodding Struc- 
ture, and is typically displayed in the Eirebol dis- 
trict, where "rods" of white quartz, varying in 
dimensions from those of telegraph poles to those of 
walking sticks, lie parallel to each other down the 
dip slope of the Moine schists. Where minerals of 
elongated habit like hornblende and biotite are 
present in the rocks showing mullion or rodding 
structure the crystals are arranged parallel to each 
other and to the dip and pitch of the folds. Cf. 
Linear Foliation. 

Mem. Geol. Surv. (N.W. Highlands), 1907, pp. 97-8, 245-7, 
and PI. xxv, facing p. 200. 

See also Geol. Mag., 1871, p. 559, fig. 2, where mullion 
structure is wrongly described as " ice-fluting." 

Multiple (Intrusions). A term applied to sills, dykes, 
laccoliths and other intrusions, formed by two or 
more successive injections of approximately the 
same magma. 

Mimipngite, David ct aliter, 1901. A variety of 
tinguaite, containing about 44 per cent, of alkali- 
felspar, 36 per cent, of nepheline and 20 per cent, 
of aegirine-augite. (Kosciusko, N.S.W.) 

T. E. W. David (et aliter} : Proc. Roy. Soc., N.S.W., xxxv, 
1901, p. 366: 

Murasakite, Koto, 1887. A schistose rock composed 
essentially of piedmontite and quartz. 

(Murasako, Japan.) 

13. Koto: Journ. Coll. Sci. Univ. Japan, i, 1887, p. 303; ii, 
1888, p. 94. 


Murbruk Structure. See Mortar Structure. 

MuSCOVadite, Winchell, 1900. --An endomorphic 
variety of norite characterised by the presence of 
cordierite and biotite. 

A. N. Winchell : Amer. Geol., xxvi, 1900, p. 294. 

Mylonite, Lapiuorth 1885. A compact chert-like 
rock, without cleavage, but with a streaky or 
banded structure ; produced W the extreme granu- 
lation and shearing of rocks which have been 
pulverised and rolled out during overthrusting, or 
by the action of dynamic metamorphism generally. 
P. Quensel : Bull. Geol. Inst. Uppsala, xv, 1916, p. 91. 
J. J. H. Teall : Proc. Geol. Assoc., xxix, 1918, p. 2 and 
Plate i. 

Mylonite-gneisS, Quensel, 1916. A rock partly granu- 
lated and partly recrystallised, intermediate in its 
characters between mylonite and schist. The 
felsic minerals show cataclastic phenomena with- 
out much recrystallisation, and often occur in 
aggregates as " augen " surrounded by and alter- 
nating with schistose streaks and lenticles of the 
recrystallised dark or mafic minerals ; = Augen- 
P. Quensel : Bull. Geol. Inst. U-psala, xv, 1916, p. 101. 

Myrmekite, Sederholm, 1899. An intergrowth of 
plagioclase and vermicular quartz, generally re- 
placing potash felspars, formed during the later 
or paulopost stages of consolidation, or during a 
subsequent period of plutonic activity. 
J. J. Sederholm : Bull. Comm. Geol. Finlande, No. 48, 1916, 
p. 63. 


Nakhlite. An achondritic meteoritic stone consisting 
of a holocrystalline aggregate of diopside, and 
olivine, with a little interstitial oligoclase, augite 
and magnetite. 
G. T. Prior : Min. Mag., xvi, 1912, p. 274. 

Napoleonite. See Corsite. 


Naujaite, Ussing, 1911. A variety of nepheline- 
sodalite-syenite rich in sodalite, and also contain- 
ing microcline and small amounts of albite, 
analcite, aegirine and soda-amphiboles ; char- 
acterised by a peculiar poikilitic texture. 

(Naujakasik, Illimausak, S. Greenland.) 
N. V. Ussing : Medd. om Gronland, xxxviii, 1911, p. 154. 

Navite, Rosenbusch, 1887. A porphyritic variety of 
olivine-dolerite, containing abundant phenocrysts 
of serpentinised olivine, with fewer of augite and 
labradorite, in a holocrystalline doleritic ground- 
mass. (Nave, Nahe Valley, Prussia.) 

Neck. A vertical plug-like body of igneous rock or 
volcanic ejectamenta, or both, representing the 
feeding channel of a volcano. = Vent. 

Nelsonite, Watson, 1907. A dyke rock composed 

essentially of ilmenite and apatite, and generally 

. containing rutile. (Nelson, Virginia.) 

T. L. Watson & S. Taber, : Bull. Geol. Surv. Virginia, iii, 

A, 1913. 

Nematoblastic, Becke, 1903. A metamorphic texture 
due to the development during recrystallisation of 
minerals like sillimanite, having a fibrous habit. 

Nepheline-basalt, Gerard, 1841. An undersaturated 
basaltic rock essentially containing nepheline, 
pyroxene, and olivine, with little or no felspar. 

Nepheline-Syenite. -- A phanerocrystalline igneous 
rock generally of granular or trachytoid texture, 
composed essentially of alkali-felspars, nepheline, 
and mafic minerals. The latter usually, but not 
necessarily, include soda-pyroxenes and amphi- 
boles ; other soda-felspathoids may be present in 
addition to nepheline, and accessory minerals 
such as zircon, sphene, apatite and others of rarer 
occurrence, are often more than usually abundant. 
A. Lacroix : Nouv. Arch., Mus. cTHist. N at., iv, 1902, p. 

F. D. Adamp & A. E. Barlow : Mem. Geol. Surv. Canada, 

No. 6 (Pub. 1082), 1910, p. 227. 
P. Quensel : Bull. Geol. Inst. U-psala, xii, 1913, p. 163. 


Nephelinite, Cordier, 1868. - - An aphanitic or por- 
phyritic rock composed essentially of augite and 
nepheline, olivine being- -bsent. If the latter 
mineral be present the rock is termed nepheline- 

Nephelitlitoid Phonolite. A general term for phono- 
lites in which felspathoids are more abundant than 

Nevadite, v. Richthofen, 1868. A porphyritic variety 
of rhyolite rich in phenocrysts. (Nevada.) 

Newlandite, Bouncy, 1899. -- A variety of griquaite 
composed of garnet, enstatite, and chrome- 
diopside. (Xewlands Diamond Pipe, S. Africa.) 
T. G. Bonney : Nat. Sci., xv, 1899, p. 177. 

Nodule. A general term for concretionary bodies, 
which can be separated as discrete masses from 
the formation in which they occur. 
G. F. Becker : U.S.G.S., Man. xiii, 1888, p. 64. 

Nonesite, Lepsius, 1878. - - A variety of porphyritic 
basalt characterised by phenocrysts of labradorite, 
augite, and enstatite, in a groundmass of plagio- 
clase and augite. (Near Mte. Cevelino, Tyrol.) 

Non-graded Sediments. A general term for detrital 
sediments, loose or cemented, containing notable 
amounts of more than one grade; e.g. , loam, 

Non-uniform Pressure. See Directed Pressure. 

J. Johnston & P. Niggli : Journ. GeoL, xxi, 1913, p. 599. 
J. Johnston : Journ. Geol., xxiii, 1915, p. 732. 

Nordmarkite, Brogger, 1890. -- A quartz-bearing 
alkali-syenite, the type-rock containing biotite and 
segirine as the chief coloured minerals. 

(Nordmarken, Norway.) 
W. C. Brogger : Zeif. f. Kryst., xvi (i), 1890, p. 54. 

Norite, Esmark. - - A phanerocrystalline rock com- 
posed essentially of labradorite and orthorhombic 
pyroxene ; if augite be present in addition the 


rock may be called either hype rite, or hypersthene- 
gabbro, according- as hypersthene or augite is the 
dominant pyroxene. 

J. H. L. Vogt : Q.J.G.S., 1909, p. Si. 

G. S. Rogers : Ann. New York Acad. Sci., xxi, 1911, p. 29. 

A. E. V. Zealley : Trans. Roy. Soc. S. A/., v, 1915, p. i. 

Norm, C.I.P.W., 1902. A term applied to the 
chemical composition of an igneous rock ex- 
pressed in terms of standard " normative " 
mineral molecules calculated from the composition 
as stated in terms of oxides ; contrasted with the 
Mode, which is the actual mineral composition, 
stated quantitatively. 

C.I.P.W. : The Quantitative Classification of Igneous Rocks, 

Normative or Standard Minerals, C.I.P.W., 1902. 

A series of ideal mineral-compounds in terms of 
which the composition of a rock may be expressed 
by a suitable manipulation of the analysis as stated 
in oxides, etc. The minerals are divided into salic 
and femic groups, and are chosen to afford a simple 
standard for comparison, complex minerals such 
as the aluminous ferromagnesian minerals being 

Northfieldite, Emerson, 1915. An ultra-quartzose 
granite containing 83 per cent, of quartz and 13 
per cent, of s,oda-orthoclase. (Northfield, Mass.) 

B. K. Emerson : Am. Journ. Sci., xl, 1915, p. 215. 

Noseanite, Boricky, 1873. A variety of felspathoid 
basalt rich in nosean, and free from felspar and 

Nosean-phpnoHte, Boricky, 1873. A variety of 
phonolite containing nosean (e.g., that of the Wolf 
Rock, Cornwall). 
J. J. H. Teall : Brit. Pet., 1888, p. 367. 

Novaculite, Cordier, 1868. An aphanitic granulose 
or cryptocrystalline rock essentially composed of 
quartz, sometimes containing other forms of 


silica, and generally accessory felspar and 
garnet ; used as ivhclslone or honestojic. 

E. F. Davis : Bull. De-pt. Geol. Univ. California, xi, p. 333, 


Obsidian. A volcanic glass, generally black, banded, 
or microspherulitic, with a glassy or satiny lustre 
and conchoidal fracture. 

F. E. Wright : Bull. Geol. Soc. Am., xxvi, 1915, p. 255. 

Obsidianite, Walcott, 1898. A term applied to small 
balls, buttons, and spheroidal and dumb-bell forms 
of dark green to black glass, often pitted and fur- 
rowed ; approximating- in composition to obsidian, 
but having generally a smaller percentage of 
alkalies. Their origin is unknown, but is prob- 
ably cosmic, as they occur in Australia and else- 
where as discrete bodies often hundreds of miles 
from any possible volcanic source. Cf. Australite, 
Billitonite, Moldavite. 

R. H. Walcott : Proc. Roy. Soc. Victoria, xi, 1898, p. 23. 

E. J. Dunn : Geol. Surv. Victoria, Bull. 27, 1912. 

H. S. Summers : Proc. Roy. Soc. Victoria, xxi, 1909, p. 423; 
see also p. 444. 

Occult Minerals, Iddings, 1913. A term applied to 
minerals which are deduced from chemical con- 
siderations to be actually or potentially present 
in a hole-crystalline igneous rock, but which for 
various reasons cannot be recognised individually. 
Thus the detection of K 2 O in a basalt suggests 
the presence of orthoclase, which may occur in 
crvstals too small for determination, or may be 
held in solid solution bv olagioclase. 
T. P. Tddings : Igneous Rocks, II, 1013, p. 19. 

Ocellar Texture, Posenbusch, 1887. A texture due 
to the tangential disposition of minerals such as 
biotite, or pyroxene, around the borders of idio- 
morphic crystals of later growth, such as analrite 
or leucite. 


Octahedrite. A group name for iron meteorites, 
which, on being etched, develop the Widtman- 
statten lines, due to the presence of kamasite and 
taenite parallel to the octahedral faces. 

Odinite, Chelius, 1892. A porphyritic dyke rock of 
basaltic composition, containing- phenocrysts of 
labradorite andi augite in a groundmass com- 
posed of felspar laths and needles of hornblende. 


Oikocryst, C.I.P.W., 1906. A matrix or host crystal 
through which smaller crystals (chadacrysts) of 
other minerals are scattered as poikilitic inclu- 

Oil Shale. A fine black or dark-brown shale contain- 
ing kerogcn (i.e., material from which crude petro- 
leum can be obtained by distillation) and char- 
acterised by having a brown streak, a leatherv 
appearance with parting-planes often smooth and 
polished, and a minutely-laminated structure. It 
differs from carbonaceous shale by curling when it 
is cut, and by its- toughness and resistance to dis- 
integration bv weathering. 
Mem. Geol. Surv. Scot. (Oil Shales of the Lothians), 2nd 

Ed., IQI2. 

H. R. J. Conacher : Trans. Geol. Soc. Glasgow, xv, 1917, 

p. 161. 
Geol. Surv. Spec. Rep. Mineral Resources of Great Britain. 

vii, 1918. 

Oje Diabase, Tornebohm. A tvpe of porphyritic 
dolerite containing long plagioclase laths in an 
aphanitic basaltic groundmass. 

Oligodasite, Bombicci, 1868. A variety of granular 
olivine-norite which has suffered a certain amount 
of alteration. The plagioclase is labradorite in 
part, generally saus&uritised, and reduced to 
oligoclase with comolementarv secondary products. 
Hvpersthene and olivine, with hornblende, chlorite, 
and bastite, as alteration products, are the char- 
acteristic mafic minerals. By recent authors the 
name oligoclasite has been given to phnnrro- 


crystalline leucocratic rocks composed chiefly of 
oligoclase, and it is in this more general sense 
that the term is now used. 

OligOSite, Turner, 1900. A phanerocrystalline rock 
composed almost entirely of oligoclase. 

Olivine-. As> a mineral qualifier this name is added to 
the names of many igneous rocks, to distinguish 
olivine-bearing types from those free from that 
mineral, e.g., Olivine -basalt, olivine-theralite, etc. 

Olivine-leucitite. = Leudte Basalt. 
Olivine-nephelinite. = Nepheline Basalt. 
Olivine Rock. = Dunite. 

Olivinite, Eichstadt, 1887. A variety of hornblende- 

picrite containing augite and anorthite. 
Ollenite, Cossa, 1881. A term applied to a variety 
of hornblende-schist characterised by abundant 
epidote, sphene, and rutile, with smaller amounts 
of garnet and other accessories. 

(Col d'Ollen, Piedmont.) 

Onkilonite, Bacldund, 1915. A variety of felspathoid- 
basalt consisting of nepheline, augite, olivine, and 
perovskite, with small amounts of leucite and inter- 
stitial glass ; felspars and iron-ores are absent. 

(Is. of New Siberia.) 

H. G. Backlund : Bull. Acad. Sci. St. Peter sbourg, 1915. 
Onyx Marble. - - A term applied to compact banded 
varieties of calcareous tufa, capable of taking a 

G. P. Merrill : Rep. U.S. Nat. Museum, for 1893, p. 593. 
Oolite. A rock made up of spheroidal or ellipsoidal 
grains formed by the deposition of successive 
coats of calcium carbonate around a nucleus. 
J. J. H. Teall : Mem. Geol. Surv. (Jurassic Rock? Britain). 

Vol. iv, 1894. 

F. M. Van Tuyl : Journ. Geol., xxiv, 1016, p. 792. 
W. H. Bucher : Journ. Geol., xxvi, 1918, p. 593. 
Ooze. A soft incoherent deep-sea deposit composed 
almost wholly of the shells and debris of foramim- 
fera, diatoms, and other organisms. Cf. Globi- 
gerina Ooze, Radiolarian Ooze, etc. 


Opacite, Vogelsang, 1872. A non-committal descrip- 
tive term suggested to avoid periphrasis, for black 
opaque grains and scales which may be iron-ores, 
or carbonaceous matter, but which are in general 
too small for individual determination by optical 

For microchemical tests see A. Brammall : Geol. Mag., 1920, 
P. 123. 

Ophicalcite, Brongniart, 1813. A variety of crystal- 
line limestone composed of calcite and serpentine. 

Ophite, Palassou, 1819. A general term applied to 
the ophitic diabases (dolerites with uralitised py- 
roxenes) occurring in the Pyrenees. 
A. Lacroix : C.R., clxv, 1917, p. 293. 

Ophitic Texture, Michel-Levy, 1877. A texture 
characteristic of dolerites, due to the penetration 
of pyroxene crystals by laths of plagioclase. A 
similar texture is sometimes developed between 
other pairs of minerals. When the pyroxene cry 
stals wholly enclose a number of plagioclase laths, 
the texture becomes a variety of poikilitic texture, 
and is distinguished by the term poikilophitic. 
A. N. Winchell : Bull. Geol. Soc. Am., xx, 1910, p. 661. 

Orbicular Structure, Delesse, 1849. - - A structure 
developed in certain phanerocrystalline igneous 
rocks (e.g., granites, diorites, and corsite), due 
to the occurrence of concentric shells of differ- 
ent mineral composition, around centres that may 
or may not exhibit a xenolithic nucleus ; = sphe- 
roidal, = nodular. 
A. C. Lawson : Bull. De-pt. Geol. Univ. California, Pub. 3, 

1904, p. 383. 
G. A. J. Cole : Sci. Proc. Roy. Dublin Soc., xv, 1916, p. 141. 

Orbite, Chelius, 1892. - - A variety of hornblende- 
porphyrite containing phenocrysts of hornblende in 
a groundmass composed essentially of laths of 
plagioclase. (Orbishohe, Odenwald.) 

Ordanchite, Lacroix, 1917. - - A variety of hauyne- 
tephrite containing phenocrysts of andesine and 
orthoclase. (Banne d'Ordanche, Auvergne.) 

A. Lacroix : C.R., clxiv, 1917, p. 582. 


Order, C.I.P.1V., 1902. A division of igneous rocks, 
considered after the division into classes, based (in 
classes I., II. and III.) on the relative pro- 
portions of normative quartz or nepheline to the 
sum of the normative felspars. This division 
is analogous to the division of rocks into 
over saturated, saturated and (as regards fels- 
pathoids) under saturated types. In classes IV. 
and V. the orders are based on the relative propor- 
tions of the normative pyroxenes, and olivine, etc., 
to the sum of the normative iron-ores and titanium 

Order of Crystallisation. A phrase loosely employed 
for the order in which the minerals of an igneous 
rock ceased to crystallise, and determined by such 
textural features as the idiomorphism of one mine- 
ral to another, and the indentation or enclosure of 
one mineral by another. Such features rarely pro- 
vide evidence of- the order in which the minerals 
began to crystallise. 

N. L. Bowen : Jour*. GeoL, xx, 1912, p. 457. 

W. Mackie : Trans. Edin. GeoL Soc., ix, 1909, p. 247. 

Ore-deposits. A general term applied to rocks con- 
taining metalliferous minerals of economic value 
in such amount that they can be profitably exploit- 
ed. By a double analogy the term is generally 
extended to include economically valuable rocks 
containing certain non-metalliferous minerals, such 
as graphite and diamond ; and also to deposits 
which, though they may not be immediately capable 
of profitable exploitation, may yet become so by a 
change in the economic circumstances that control 

their value. 


Orendite, Cross, 1897. - - A phanerocrystalline rock 
composed of leucite and sanidine, with phlogopite 
and augite, and therefore a plutonic equivalent of 
W. Cross : Am. Journ. Set., iv, 1897, p. 123. 


OrganogenotlS, Renevier, 1880. A group name 
applied to rocks of organic origin. 

Ornoite, Cederstrdm, 1893. - - A term applied to a 
variety of hornblende-diorite, the chief member of 
a suite of rocks in which the felspar varies from 
oligoclase to labradorite as the proportion of horn- 
blende increases. The rock thus passes into horn- 
blende-gabbro, and by decrease of felspar into 
hornblende-picrite. (Orno, Sweden.) 

Orthoclase-gabbro, Pumpelly, 1880. -- A descriptive 
name for rocks now known as monzonite, in which 
the plagioclase is at least as calcic as labradorite ; 
= Gabbro-syenite. Cf. Granogabbro. 

Orthociasite, Merioin, 1915. A medium to fine- 
grained dyke-rock containing about 90 per cent, or 
more of orthoclase. 

U.S.G.S., Prof. Pap. 87, 1915, p. 40. 

Orthofelsite, Teall, 1888. A rock containing porphy- 
ritic orthoclase in a felsitic groundmass, pheno- 
crysts of quartz being absent ; = Orthophyre. 

J. J. H. Teall : British Petrography, 1888, p. 291. 

Orthogneiss, Roseribusch, 1898. A general term ap- 
plied to gneisses derived from rocks of igneous 
origin; contrasted with paragneiss (q-v.). 

Orthophyre, Coquand, 1851. = Orthoclase Por- 

Orthophyric Texture, Rosenbusch, 1896. A ground- 
mass texture distinguished from trachytic texture 
by the presence of abundant stumpy rectangles of 

Orthosite, Turner, 1900. A hololeucocratic phanero- 
crystalline rock composed almost entirely of ortho- 

Ortlerite, Stache & John, 1879. A variety of horn- 
blende-porphyrite containing phenocrysts of horn- 
blende in a holocrystalline felspathic groundmass. 

(Mte. Confinale, Tyrol.) 


Ossypite, Hitchcock, 1871. A coarse-grained variety 
of troctolite composed of labradorite, olivine, and 
magnetite, with a little diallage. 

(Waterville, New Hampshire.) 

Ostraite, Duparc, 1913. A variety of ariegite char- 
acterised by abundant magnetite and spinel. 

(Ostraia Sopka, Urals.) 
L. Duparc : Bull. Soc. franf. Min., xxxvi, 1913, p. i. 

Ottajanite, Lacroix, 1917. - - A variety of leucite-te- 
phrite richer in plagioclase and poorer in leucite 
than vesuvite. Corresponds in chemical composi- 
tion to sommaite. (Ottajano, Mte. Somma.) 
A. Lacroix : C.R., clxv, 1917, p. 485. 

Ottrelite-schist. A schistose rock characterised by 
abundant porphyroblastic or embryo-crystals of 
ottrelite. (Ottrez, Ardennes.) 

Ouachitite, Kemp, 1890. An olivine-free variety 
of monchiquite characterised by abundant biotite. 
G. H. Williams: GeoL Surv. Arkansas Ann. Re-p., ii, 1890, 
p. 107. 

Ouenite, Lacroix, 1911. -- A fine-grained eucrite-like 
rock containing green augite and anorthite with 
smaller quantities of hypersthene and olivine. 
Both melanocratic and leucocratic varieties occur. 

(Ouen, New Caledonia.) 
A. Lacroix: C.R., clii, 1911, p. 816. 

Oversaturated, Shand, 1915. -- A term applied to 
igneous rocks which contain free silica (quartz, 
tridymite, etc.) of magmatic origin. 

S. J. Shand : GeoL Mag., 1913, p. 508. 

A. Holmes: GeoL Mag., 1917, p. 119. 

Oxygen Ratio, Bischof. - - The figure expressing the 
following ratio, calculated from the molecular pro- 
portions of the constituents of a mineral or rock 

Number of atoms of oxygen in the basic oxides. 

Number of atoms of oxygen in SiO 2 - 
Cf. Coefficient of Acidity. 


Ozokerite. A compact, waxy, natural hydrocarbon of 
various colours, but generally jet-black ; soluble in 
turpentine and chloroform = mineral wax = native 
paraffin. (Galicia.) 

Pacific Suite, Harker, 1896. A general term for the 
whole assemblage of calc-alkali-rocks, notably re- 
presented by andesites, granodiorites, and asso- 
ciated rocks ; directing attention to their distribu- 
tion around the Pacific, to their association with 
Pacific types of coast-line, and more generally to 
their association with tectonic structures of the 
mountain-building type due to compression, fold- 
ing, and overthr ust ing. Cf. Atlantic Suite. 

Pahoehoe, Dutton, 1883. An Hawaiian term for fluent 
or ropy lava consisting of wrinkled, corded, hum- 
mocky flows free from the jagged and scoriaceous 
masses characteristic of block-lava ; Dermolithic 
lava. Cf. Aa-lava. 

Paisanite, Osann, 1893. = riebeckite-micro granite; 

riebeckite-quartz-keratophyre ; = ailsyte. 

(Paisano Pass, Texas.) 

Palagonite, W alter shaus en, 1853. A term applied to 
altered basaltic glass, occurring interstitially, as 
amygdale fillings, or in tuffs. Palagonite is a 
soft, brown or greenish-black cryptocrystalline 
substance. (Palagonia, Sicily.) 

J. J. H. Teall: Q.J.G.S., liii, i8q 7 , p. 48=;. 

Palatinite, Laspeyres, 1869. A term applied to basal- 
tic and dioritic rocks containing orthorhombic 

A prefix, used particularlv by Continental au- 
thors, to indicate the pre-Tertiarv age, and gener- 
ally altered character, of the rock to the name of 
which is added; e.g. , paltzopicrite. By some 
writers the term palceo has been further restricted 


to pre-Carboniferous rocks, those of pre-Tertiary 
and post-Devonian age being- indicated by the 
prefix 111 c so-. 

Paleotypal, Brdgger, 1894. A general term applied to 
aphanitic and porphyritic igneous rocks having the 
habit or suite of characteristics typical of altered 
volcanic and hypabyssal rocks such as many of 
those of pre-Tertiary age. By decomposition 
felspars have lost their original lustre, and glass, 
where present, has become dull through devitrifica- 
tion. Rocks having the younger-looking aspect of 
fresh volcanic rocks are described as cenotypal 


Palimpsest Structure, Sederholm. -- A structure of 
metamorphic rocks due to the presence of remnants 
of the original texture of the rock. 

Palingenesis, Sederholm, 1907. - - The rebirth of a 
magma in situ by the fusion of pre-existing rocks 
such as granites, gneisses and schists. 
J. J. Sederholm : Bull. Comm. G6ol. Finlande, 23, 1907, p. 

Pallasite, Rose, 1862. A group name for siderolites, 
containing fractured or rounded crystals of olivine 
in a network of nickel-iron. 

Pan-idiomorphic, Roseribusch. A textural term ap 
plied to rocks in which almost all the constituents 
are idiomorphic. 

Pantellerite, Forster, 1881. - - An alkali-rhyolite or 
quartz-soda-trachyte (according to the abundance 
of quartz), containing anorthoclase, aegirine and 
cossyrite. (Pantelleria, Mediterranean.) 

H. S. Washington: Journ. Geol., xxi, 1913, p. 653, p. 683; 
xxii, 1914, p. 16. 

Paragenesis. -- A term connoting the association of 
minerals in characteristic suites considered in rela- 
tion to their origin, and implying a deduction of 
the processes by which each suite has developed, 
or of the order of formation or alteration of 
the minerals present in the suite. 


Paragneiss, Rosenbusch, 1901. -- A term applied to 
gneisses formed from detrital sediments such as 
arkose ; contrasted with ortho gneiss (q.v.). 

Paramagnetism, Faraday, 1845. A property of man} 
substances, akin to ferromagnetism, in virtue of 
which, when placed in a non-uniform magnetic 
field, they tend to move towards the strongest part. 
Permanent magnetism is practically absent, and 
the susceptibility, which is far smaller than that of 
iron, is constant at any given temperature, but is 
in most substances nearly inversely proportional to 
the absolute temperature. Cf. diamagnetism. 
For the application of the magnetic properties of minerals to 

their separation see 
T. Crook : Science Progress, No. 5, 1907, p. 30. 

Paulopost, Evans, 1916. A general term applied to 
changes suffered by igneous rocks immediately 
after their formation, the changes being a direct 
consequence of the consolidation of the magma 
(e.g., albitisation, serpentinisation) ; = Penecon- 
temporaneous D enteric. 

Peach. A local Cornish name for rocks produced by 
the alteration of the walls of tin-lodes, and con- 
sisting of quartz with chlorite or tourmaline. 

Pegmatite, Haiiy, 1822. A term applied to graphic- 
granite, and extended to coarse-grained modifica- 
tions of granite characterised by irregular segre- 
gation of particular minerals rather than by inter- 
penetration. The term has also been applied to 
other igneous rocks whose names are used as a 
prefix, e.g., syenite-pegmatite. 

W. O. Crosby & M. L. Fuller : Technology Quarterly, ix, 
1896, p. 326. 

J. V". Elsden : Geol. Mag., 1904, p. 308. 

L. Duparc : Mem. Soc. Phys. et d'Hist. Nat. Geneva, xxxvi, 
Pt. 3, 1910, p. 283. 

E. S. Bastin : Journ. Geol., xviii, 1910, p. 297. 
- U.S.G.S. Bull. 445, 1911. 

F. F. Grout : Econ. Geol., xiii, 1918, p. 185. 


Pegmatoid, Evans, 1912. A term suggested to 
denote very coarse-grained facies of igneous rock 
having a pegmatite-habit, but differing from peg- 
matite proper by the absence of graphic texture. 

Pelagite. A term applied to the manganese nodules 
and concretions of deep-sea deposits ^ Halobolit e. 
11 Challenger " Rep. (Deep Sea Deposits), 1891, p. 341. 

Pelite, Naumann. - - A general term for clastic sedi- 
ments composed of clay, minute particles of 
quartz, or rock-flour. A volcanic ash of corres- 
ponding grade is called pelitic tuff. 

Pencatite. - - A crystalline limestone containing bru- 
cite ; calcife and brucite being in approximately 
equal molecular proportions (63 per cent, and 37 
per cent, respectivelv). Cf. Predazzite. 
A. Harker : Mem. Geol. Surv. (Tert. Tg. Rocks, Skye), 1904, 
P. 150- 

Peperino. A local Italian name for a soft incoherent 
yellow-grey tuff, containing broken crystals of fel- 
spar, leucite, biotite, and augite, and numerous 
rock-fragments embedded in a finely-granular 

Per-, C.I.P.W., 1902. A prefix indicating that one 
factor is present in extreme amount, its ratio to 
another factor being greater than 7/1 ; e.g., 
peralcalic, persalic, etc. 

Peridotite, Rosenbusch, 1877. -- A general term for 
non-felspathic phanerocrystalline rocks, consisting 
of ollvine, with or without other mafic minerals. 
Spinellids are the usual accessories. 

J. W. Judd : Q.J.G.S., xli, 188=;, p. 354. 

A. Harker : Mem. Geol. Surv. (Tert. Tg. Rocks, Skye), 1904, 
pp. 63 and 374. 

Mem. Geol. Surv. Scot. (Small Isles), 1908, p. 79. 

Perknite, Turner, 1901. -- A general term for rocks 
composed essentiallv of pyroxenes or amphiboles, 
or of members of both groups. 
TT. W. Turner : Jonrn. Geol., ix, 1907, p. 507. 


Perlite. A glassy volcanic rock of rhyolitic compos! 

tion with marked perlitic structure. 
W. W. Watts : Q.J.G.S., 1, 1894, p. 367. 

Perlitic Structure. A structure produced in homo- 
geneous material by contraction during- cooling, 
and consisting of a system of irregular, convolute, 
and spheroidal cracks; generally confined to 
natural glass, but sometimes found in quartz, and 
other non-cleavable minerals, and as a relict 
structure in devitrified rocks. 
W. W. Watts : Geol. Mag., 1894, p. 379. 

Permanent Set. The permanent change of shape of 
a plastic substance due to its imperfection of elas- 
ticity, i.e., to the incompleteness of its recovery 
after being stressed. 

Persilicic, Clarke, 1911. -- A term suggested to re- 
place the term acid as applied to igneous rocks ; 
for intermediate and basic the corresponding terms 
are mediosilicic and subsilicic, respectively. 
Petrogenesis. -- A branch of Petrology which deals 
with the origins of rocks, and more particularly 
with the origins of igneous rocks. 

J. P. Tddings : Bull. Phil. Soc. Wash., xii, 1892, p. 89. 

C. Doelter : Die Petrogenesis, 1906. 

J. P. Id'dings : Prof. Am. Phil. Soc.. 1, 1911, p. 286. 

A. Harker : Brit. Ass. Re-p. (1911). 1912, p. 370. 

R. A. Daly : Igneous Rocks and their Origin, 1914. 

A. Harker : Q.J.G.S., Ixxiii, 1917, p. Ixvii. 

A. Holmes: Geol. Mag., 1916, p. 268. 

- Q.J.G.S., Ixxii, 1916, p. 271 : and Ixxiv . 1918, pp. 51 and 


Petrogratjhical Province, Judd, 1886. A natural re- 
gion in which the rocks belonging to a definite 
cvcle of igneous activity are characterised bv speci- 
fic peculiarities collectively as well as individually, 
which distinguish them from other assemblages 
of rocks belonging to other regions or cycles. 
The possession by the rocks of certain common or 
related features as regards chemical and mineral 
composition, structure and texture, mode of oc- 


currence, alterations, associated ore-deposits, and 
attendant metamorphic phenomena, is interpreted 
to imply community of origin and similarity of 
evolution. In any given Petrographical Province 
a similar succession of processes, dependent on 
the preceding geological history of the region, is 
considered to have acted on similar suites of the 
raw materials from which the related igneous rocks 
were evolved. Thus there is necessarily some 
overlapping of adjacent Provinces both in space 
and time, and it is rarely that a Province as a 
whole can be clearly defined in terms of well- 
marked boundaries. = Comagmatic Region. 
Cf. Consanguinity. 

J. W. Judd : Q.J.G.S., xlii, 1886, p. 54 (Bohemia and Hun- 
J. P. Iddings : Bull. Phil. Soc., Wash., p. 128, 1892. 

Journ. Geol., i, 1893, p. 166 (Andes). 

W. C. Brogger : Eru-ptivgest. Kristiania, i, 1894: ii, 1895; 

iii, 1898. 
H. S. Washington : Journ. Geol., vii, 1899, p. 463 (Essex 

Co., Mass.). 

Bull. Geol. Soc. Am., xi, 1900, p. 389 (Magnet Cove, 

T. H. Holland : Mem. Geol. Surv. India, xxviii, Pt. 2, TQOO 

(Charnockite Series). 
A. Lacroix : Nouv. Arch, du Mus. d^Hist. Nat., 4 Ser., i and 

v, 1902-3 (Madagascar). 
G. T. Prior : Min. Mag., xiii, 1903, p. 233 (Brit. E. Africa 

and Atlantic Is.). 

F. W. Adams : Journ. Gcol., xi, 1903, p. 239 (Monteregian 

A. Harker : Mem. Geol. Surv. (Tert. Ig. Rocks, Skye), 1904. 

L. V. Pirsson : Am. Journ. Sci., xx, 1905, p. 35 (Montana). 

H. S. Washington : Carnegie Inst., Washington, Pub. 57, 
1906 (Roman District). 

Trans. Am. Inst. Min. Eng., xxxix, 1909, p. 735 


A. Harker : Nat. Hist. Ig. Rocks, 1909, p. 88 (General). 

N. V. Ussing : Medd. om Grdnland, xxxviii, 1910 (Green- 

G. S. Rogers: Ann. New York Acad. Sci., xxi, 1911, p. 11 
(Cortlandt Series). 

G. W. Tyrrell : Geol. Mag., 1912, pp. 69 and 120 (late Paleo- 
zoic, Scotland). 


H. H. Robinson : U.S.G.S., Prof., Paf. 76, 1913 (San 
Francisco Volcanics). 

M. Stark : Fort, der Min. Krist. u. Pet., iv, 1914, p. 251 
(General and bibliography). 

J. J. O'Neill : Geol. Surv. Canada, Mem. 43 (Pub. No. 1311), 
1914 (Monteregian Hills). 

W. Cross : U.S.G.S., Prof. Paf., 1915 (Hawaii). 

R. A. Daly : Bull. Geol. Soc. Am., xxvii, 1916, p. 325 
(Pacific Is.). 

A. Holmes : Q.J.G.S., Ixxii, 1916-17, p. 260 (E. Africa). 

Min. Mag., xviii, 1916, p. 70 (Angola). 

A. Harker : In Handbucli der Regionalen Geologic, iii, 

i, 1918 (British Isles). 
Q.J.G.S., Ixxiii, 1917-18, p. Ixvii (British Is.V 

A. Holmes : Min. Mag., xviii, 1918, p. 180 (Arctic Is.). 
Petrography. - - A general term for the systematic 
description of rocks, based on observations in the 
field, on hand-specimens and on thin sections. 
Petrography is thus wider in its scope than 
Lithology, but more restricted than Petrology, 
which implies interpretation as well as description. 
In their French usage, however, the terms petro- 
graphie and Hthologie are synonymous. 
Petrology. A general term for the study by all avail- 
able methods of the natural history of rocks, in- 
cluding their origins, present conditions, altera- 
tions and decay. Petrology comprises petro- 
graphy on the one hand, and petrbgenesis on the 
other, and properly considered, its subject matter 
includes ore-deposits and mineral deposits in gene- 
ral as well as " rocks " in the more limited sense 
in which that term is generally understood. 

Petrosilex. See Felsite. 

Phacolith, Harker, 1909. A concordant minor intru- 
sion occupying the crest or trough of a fold. Un- 
like a laccolith, its form is the consequence of fold- 
ing, 'not the cause. 
A. Harker : Nat. Hist. Ig. Rocks, 1909, p. 77. 

Phanerocrystalline. A term applied to igneous rocks 
in which all the crystals of the essential minerals 
can be distinguished individually by the naked eye ; 
contrasted with aphanitic. 


Phase, Gibbs. A homogeneous part of any system of 
substances which is mechanically separable from 
every other homogeneous but dissimilar part of 
the system (e.g., a vapour, a solution, or a cry- 
stal). Cf. Component. 

Phase Rule. A thermodynamic generalisation which 
states that in any system 

P+f = n+2. 
where P denotes the number of co-existing- phases 

in the system ; 

f denotes the degrees of freedom; and 
n denotes the number of independent components 

which compose the system. 
A. Findlay : The Phase Rule, London, 1918. 

PhenocrystS, Iddings, 1892. A general term applied 
to the large megascopically visible crystals of por- 
phyritic rocks. 

L. V. Pirsson : Am. Journ. Set., vii, 1899, p. 271. 

T. L. Watson : Journ. Geol., ix, 1901, p. 97. 
Phonolite, Klaproth, 1 80 1. An aphanitic rock with 
or without phenocrysts), consisting of alkali-fel- 
spars and felspathoids, with pyroxenes and amphi- 
boles, the mafic minerals being generally soda- 
bearing varieties. 

G. T. Prior : Min. Mag., xiii, 1902, p. 237. 

Phosphorite. - - A term applied to concretionarv 
masses or metasomatised rocks, consisting- mainly 
of calcium phosphate (hydro- or fluo-calcium car- 
bono-phosphate) . 

O. Stutzer : Zeit. f. Prakt. GeoL, xix, 1911, p. 73. 
A. L. du Toit : Geol. Surv. S. Af. Mem., 10, 1917. 

PhreatlC, Daubree, 1887. A term applied to ground- 
waters, i.e., to seepage waters occurring at and 
below the water-table, drainage waters above the 
water-table being- called vadose. 
R. A. Daly : Econ. Geol., xii, 1917, p. 494. 
Phtanite, Haily. A term applied to compact crypto- 
crystalline silicified shales and other siliceous rocks 
such as lydite, hornstone, etc. =Phthanitc. 
G. F. flecker: U.S.G.S., Mon. xiii, 1888, p. 105. 


Phyllite, Naumann. - - A compact lustrous schistose 
rock with its minerals less well defined than in a 
mica-schist, the characteristic mineral by which 
the foliation is controlled being sericite. 

Picrite, Tschermak, 1866. A melanocratic rock which 
differs from peridotite in containing a small amount 
of felspar (usually labradorite). The term has also 
been extended to include similar rocks, often asso- 
ciated with teschenites, in which analcite is pre- 
sent. These should be distinguished as Analcite- 

G. W. Tyrrell: Q.J.G.S., Ixxii, 1916-17, p. 84. 

A. Holmes : Geol. Mag., 1917, p. 150. 

Picrite-basalt. A melanocratic basalt characterised 
by abundant micro-phenocrysts of olivine and au- 
gite, in a groundmass containing only a small pro- 
portion of labradorite ; = Felspathic limburgite. 
A. Holmes : Q.J.G.S., Ixxii, 1916-17, p. 244. 

Pieiiaarite, Brouwer, 1910. A melanocratic variety 
of aegirine-foyaite characterised by exceptional 
richness in sphene. (Bushveld.) 

Piezocrystallisation, Weinschenk, 1900. A term ap- 
plied to the crystallisation of a viscous and con- 
strained magma during the operation of powerful 
directed pressure, the latter condition implying 
that the normally-formed pyrogenetic minerals 
may not be stable as they would be under condi- 
tions of hydrostatic pressure. 
E. Wienschenk : Cong. Geol. Inter., C.R., \iii (1900), p. 326. 

Pilandite, Henderson, 1898. A variety of porphyry 
characterised by the abundance of anorthoclase as 
phenocrysts and in the groundmass; the porphy- 
ritic equivalent of hatherlite. 

(Pilandsberg, Bushveldt.) 

Pillow Lavas, Bonney, 1893. A general term applied 
to basaltic or albitised basaltic rocks that exhibit 
ellipsoidal or pillow structure. 

H. Dewey & J. S. Flett : Geol. Mag., 1911, p. 202, p. 241. 

J. V. Lewis : Bull. Geol. Soc. Am., xxv, 1914, p. 595. 


Pilotaxitic Texture, Rosenbusch, 1887. A texture, 
developed typically in the groundmass of certain 
undesites, due to a felt-like interweaving of felspar 
microlites ; probably a variety of micropoikilitic 
texture in which the host mineral is generally 

PhlOlite, Rumpf, 1873. A metamorphic rock contain- 
ing crystals and granular aggregates of magnesite 
(breunnerite variety) in a schistose matrix which 
may be phyllite or talc-schist. The rock derives 
its name from the resemblance of the magnesite 
bodies to pine cones. (Styria.) 

T. Crook : Trans, Ceramic Soc., 1919^ P- 81. 

Pipe-amygdales, Cohen, 1875. ~- Amygdales of pipe- 
like form extending upwards with swellings or 
bifurcations from the base of a lava-flow 7 , to which 
they may be normal or inclined. The form and 
location of these amygdales are probably due to the 
flow of lava over a moist floor. 
A. L. Du Toit : Geol. Mag., 1907, p. 13. 

Piperno. A local Italian name given to the trachytic 
tuffs or eutaxitic trachytes of the Phlegrean Fields. 

Pisolite. A coarse-grained variety of oolite made up 
of oolite-grains of about the size of a pea. 

Pitchstone. A term applied to more or less devitrified 
glassy igneous rocks of various compositions, 
characterised externally by a dull pitch-like lustre, 
and internally by the presence of crystallites. 
Rhyolite-, dacite-, andesite-, and other varieties of 
pitchstone are distinguished when evidence of 
composition is available. 

A. Scott : Trans. Geol. Soc. Glasgow, xv, 1914, p. i. 
E. M. Anderson & E. G. Radley : Q.J.G.S., Ixxi, 1915, p. 

Plagiaplite, Duparc & Pearce, 1902. - - A dioritic 
aplite containing oligoclase or andesine with sub- 
ordinate amounts of hornblende and micas. By 
the incoming of quartz the type passes into glad- 
kaite. ' (Koswa, N. Urals.) 

L. Duparc & P. Pamfil : Bull. Soc. franf Min., xxxiii, 1910, 
P- 366. 


Plagiophyre, Tyrrell, 1912. -- A term for rocks 
resembling orthophyres in texture, but containing 
plagioclase instead of orthoclase. The type 
example contains laths of andesine with interstitial 
chloritic minerals, iron-ores, and, in places, ortho- 
clase. Cf. Leucophyre. 

(Carrick Hills, Ayrshire.) 
G. W. Tyrrell : Trans. Geol. Soc. Glasgow } xv, 1912-13, p. 77. 

Planophyric, C.I.P.W., 1906. A term applied to por- 
phyritic rocks in which the phenocrysts are ar- 
ranged in layers. 

Plasticity. The property of a substance whereby it 
can be permanently deformed without rupture. A 
plastic solid is one in which recovery from a state 
of strain is only partial. The permanent deforma- 
tion thus produced is called permanent set. The 
stress just necessary to cause permanent set is 
called the elastic limit, and a body strained beyond 
this limit flows until the stresses are reduced be- 
low it. When the elastic limit is zero, as in 
pitch, and permanent set is acquired at a rate pro- 
portional to the shearing-stress applied, the plas- 
ticity (viscosity of some authors) is described as 

L. Milch : Geol. Rund., ii, 1911, p. 145. 

F. D. Adams & J. A. Bancroft : Journ. Geol., xxv, 1917, 
P- 597- 

H. Jeffreys : See Geol. Mag., 1916, p. 126. 

Platy Structure. A structure due to differential con- 
traction during cooling, occurring in lavas and in- 
trusions as a series of fractures parallel to the 
cooling surface. Igneous rocks may thus be 
cracked into thin plates or tabular sheets, which 
give them a stratified appearance, especially as 
seen in the field when the structure has been 
developed by weathering. 

Plauenite, Brogger, 1895. The type syenite of 

Plauen, near Dresden. 
H. S. Washington : Am. Journ. Sd., xxii, 1906, p. 132. 


Pleochl'OlC Haloes. A term applied to coloured zones 
occurring around radioactive inclusions (e.g., zir- 
con) in certain minerals (e.g., micas, tourmaline, 
cordierite), characterised by darker tints than the 
enclosing mineral, by pleochroism, and by a zoned 
structure. The zones are parallel to the periphery 
of the inclusion, about which they have developed 
as a consequence of the emission of a - particles 
(helium atoms, positively charged) from the radio- 
active elements contained in it. = Radio-haloes. 
J. Joly : Phil. Mag., xix, 1910, pp. 321 & 630; xxv, 1913, 
p. 644. 
Phil. Trans. Roy. Soc., ccxviiA, 1917, p. 51. 

Plumasite, Lawson, 1903. A phanerocrystalline rock 
consisting essentially of oligoclase and corundum. 

(Plumas Co., California.) 

A. C. Lawson : Bull. De-pt. Geol. Univ. California, iii, 1903, 
p. 219. 

"Plus" Minerals, Lcewinson-Lessing, 1897. A term 
applied to minerals (such as felspars) whose mole- 
cular volumes are greater than the sum of the 
molecular volumes of the constituent oxides. In 
the case of allotropic modifications of the latter, 
that having the larger molecular volume is used in 
the calculation. Cf. " Minus " Minerals. 
F. Lcewinson-Lessing : Cong. Geol. Inter., C.R., vii, 1897, 
p. 194. 

Plutonic- A general term applied to major intrusions 
and to the rocks of which they are composed, sug- 
gestive of the depths at which they were formed 
in contradistinction to most minor intrusions and 
all volcanic rocks. 

Pneumatolysis, Buns en. The process whereby mine- 
rals (whether occurring in ore-deposits or not) are 
produced wholly or in part from volatile com- 
pounds of one or other of their constituents, the 
agents concerned being the magmatic gases known 
as miner alisers. 
A. Harker : Nat. Hist. Ig. Rocks, 1909, p. 282. 

Poecilitic Texture. See Poikilitic. 


Poikilitic Texture, Williams, 1886. - - A texture in 
which small granular crystals are irregularly scat- 
tered without common orientation in larger crys- 
tals of another mineral. The term has also been 
applied to the variegated marls of the Trias. 
G. H. Williams : Journ. Geol., i, 1893, p. 176. 

Poikiloblastic. Becke, 1903. A metamorphic texture 
due to the development, during recrystallisation, of 
a new mineral around numerous relics of the 
original minerals, thus simulating the poikilitic 
texture of igneous rocks. When the included 
relics also reveal the original texture of the rock, 
the new texture is helicitic (<J.^-)- 

PoikiloohitlC Texture, Johannsen, 1911. - - A term 
suggested for a varietv of ophitic texture in 
which the pvroxenic matrix completelv includes 
laths of plagioclase, and is not merely penetrated 
by them. 

Pollenite. Lacroix, IQO7. A heteromorphic variety of 
campanite containing orthoclase. subordinate 
olioDclase, sodalite, and nepheline, with biotite, 
olivine, melanite, and sphene. 

(Pollen a, Mte. Somma.) 
A. Lacroix : Nouv. Arch, du Mus. (THist. Nat., ix, 1907, 

P- 137- 

Polzenite, Scheumann, 1913. A variety of melilite- 
basalt. (Polzen, Bohemia.) 

Ponzite, Washington, 1913. A term suggested for 
trachytes of the Ponza type (Rosenbusch) ; charac- 
terised by the presence of pyroxene (diopside and 
Eegirine-augite) as the chief mafic mineral. 

Porcellanite. A compact thermallv-metamorphosed 
rock of light colour and porcelain-like appearance, 
derived from marls or shales. 

Porfido rosso antico. The withamite-bearing horn- 
blende-porphyrite of Djebel Dokhan in Egypt. 

Porosity. The ratio, P, expressed as a percentage, of 
the volume, V p , of the pore-space in a rock to the 



volume, V r , of the rock, the latter volume includ- 
ing- rock material plus the pore-space. 
P == 100 V p /V r . 

J. Allen Howe : The Geology of Building Stones, London, 

iQ'o, p. 313- 
A. L. Du Toit : Trans. Roy. Soc., S. Africa, iv, 1915, p. 

A. Holmes : The Geological and Physical Characters of 

Concrete Aggregates, B.F.P.C. Red Book. 256, 1920, p. 

133. Petro graphic Methods and Calculations, 1920. 

Porphyrite. A term which has been variously used 
for pre-Tertiary andesitic rocks, altered andesite 
rocks, and hypabyssal rocks of marked porphyri- 
tic texture and andesitic composition. The last 
usage referred to is that now customary. The 
phenocrvsts are generally plagioclase (average 
composition that of andesine) and mafic minerals, 
and the groundmass is holocrvstalline and more 
coarsely grained than in andesite. To avoid con- 
fusion some writers prefer terms such as diorite- 
porphyry and andesite-porphyry. Cf. Porphyrv. 

Porphyritic Texture. A texture of igneous rocks due 
to the presence of crystals (phenocrvsts) which are 
conspicuously larger than the mineral individuals 
of the groundmass through which they are sprin- 

Porphyroblast, Becke, 1900. - - A term given to the 
pseudo-porphyritic crystals of rocks produced by 
thermodynamic metamorphism. The correspond- 
ing texture is called porphyroblastic. 

Porphyroclastic Structure, Becke, 1903. - - See 

Mortar or Murbruk Structure. 
Porphyro-granulitic Texture, Judd, 1885. A texture 

of certain dolerites which contain phenocrysts of 
felspar and olivine in a base of lath-shaped fel- 
' spars and irregular grains of augite ; i.e., a com- 
bination of porphyritic and intergranular textures. 
J. W. Judd : QJ.G.S', xli. 1885, p. 761. 
Porphyroid, Los sen, 1869. -- A term applied to 
porphyroblastic metamorphic rocks intermediate 


structurally between hallefiinta and granite-gneiss, 
in the same way as quartz-porphyry or granite- 
porphyry are intermediate between rhyolite and 
granite. The term has been extended to include 
porphyroblastic schists of sedimentary origin. 
P. Quensel : Bull. Geol. Inst. U-psala, xii, 1913, p. 265. 

Porphyry. A term first given to an altered variety of 
porphyrite (porphyrites lapis) on account of its 
purple colour, and afterwards extended by com- 
mon association to all rocks containing conspicu- 
ous phenocrysts in a fine-grained or aphanitic 
groundmass. The resulting texture is described 
as porplivritic. In its restricted usage, without 
qualification, the term porphyry usually implies a 
hypabyssal rock containing 1 phenocrysts of alkali- 
felspar, though in the field it is generally allowed 
a wider scope, and commercially it is used for all 
porphyritic rocks. With mineral- and rock-name 
qualifiers it is used in combinations such as quartz- 
porphvrv, nepheline-porph\iry, granite-porphyry, 
etc., while in an amputated form, -phyre, first intro- 
duced by Brongniart in 1813, and used as a suffix, 
it appears in terms such as mclaphyre, lampro- 
phyre, leucitophyre, etc. 

Prasinite, Kalkowsky, 1886. A variety of green 
schist, in which hornblende, chlorite, and epidote 
are present in approximately equal proportions. 

Predazzite, Petzlioldt. - - A variety of dedolomitised 
crystalline limestone containing- brucite, the latter 
mineral being in less amount than in pencatite, in 
which the molecular proportions of CaO : MgO 
are those of dolomite. (Predazzo, Tyrol.) 

A. F. Rogers : Aw. Joitrn. Sci., xlvi, 1918, p. 582. 

Primary Igneous Gneiss, Harker. See Gneissose 

Propylite, v. Richthofen, 1868. - - A name given to 
hydrothermally-altered varieties of andesite or 
dacite ; generally containing secondary calcite and 
silica, chlorite and sulphides. 
J. W. Judd : Q.J.G.S., xlvi, 1890, p. 341. 


Propylitisation. - The late-mag-matir processes, in- 
volving- the introduction of carbon-dioxide, 
sulphur, and water, whereby andesitic and related 
rocks are altered. 

Proteolite, Boase, 1832. An old term for hornfelsic 
rocks. Bonney proposes to revive the term for 
hornfels composed of quartz, mica, and andalusite. 
Cf. Cormibianite. 
T. G. Bonney : Q.J.G.S., xlii, 1886. p. 104. 

Proterobase, Gunibel, 1874. An altered doleritic or 
basaltic rock containing- purple-brown aug-ite and 
primary brown hornblende, and characterised bv 
the presence of secondary green hornblende and 
other alteration products. The rock to which the 
name was first applied is a Silurian diabase in the 

J. S. Flett : Mem. Geol. Surv., 335-336 (Padstow and Camel- 
ford), IQIO, p. 43. 

Protoclastic Structure. A structure produced by the 
granulation of minerals of early formation, the 
granulation being- due to differential flow of the 
partlv consolidated mag-ma from which the frac- 
tured minerals separated. 

Protogenqus, Naumann, 1858. -- A group name for 
" original " rocks as opposed to "derived" rocks, 
and including- saline deposits, coal, igneous rocks, 
and ore-deposits. The term is no longer used. 
Cf. D cut erogenous. 

Protogine, ]urine, 1806. A term applied to the cen- 
tral granite of the Alps, which, being gneissose in 
structure, and containing sericite, chlorite, epidote 
and garnet, is considered to be of composite ori- 
gin or else to have crystallised, or in part to have 
recrvstallised, under stress during or after con- 

L. Duparc et L. Mrazec : Arch. Sci. Ph-ys. et Nat., Geneva, 
v, 1898. 

Protomylonite, Backlund, 1918. - - A mylonitic rock 
produced from contact-metamorphic rocks, granu- 
lation and flowage being due to overthrusts 


following, in the first place, the contact-surfaces 
between the intrusion and the country-rock. The 
first rocks to be crushed and rolled out during- the 
process are thus the metamorphic rocks already 
produced in contact with the intrusion. 
II. G. Backlund : Geol. For. Fork., xl, 1918, p. 195. 

Prowersite, RosenbuscK^ 1908, after Prowersose, 

Cross, 1906. A syenitic lamprophyre of fine grain, 
containing- abundant biotite and orthoclase, with 
smaller amounts of augitej^ altered olivine, and 
iron-ore minerals. A variety containing porphy- 
ritic perthite is also known. 

(Prowers Co., Colorado.) 
W. Cross : ] ourn. Geol., xiv, 1906, p. 165 ; see also p. 173. 

Psephicity, Mackie, 1897. - - The degree of " round- 
ness " characterising pebbles or sand-grains. The 
coefficient of psepliicity is the ratio of specific 
gravity to hardness, and roughly expresses the 
relative facility with which minerals can be 
W. Mackie : Trans. Edin. Geol. Soc., vii, 1897, p. 301. 

Pseudo-Conglomerate. An autoclastic conglomerate 
formed by fragmentation and rolling nearly in situ, 
due to the action of orogenic forces ; = Crush-con- 

Pseudo-porphyritic. A metamorphic texture due to 
the development during recrystallisation of large 
well-defined crystals, such as those of garnet in 
mica- and chlorite-schists ; = Porphyroblastic. 

Psettdotachylyte, Shand, 1914. A black rock exter- 
nally resembling tachylyte and occurring in irre- 
gularly branching veins. The material carries 
fragmental enclosures, and shows evidence of 
having been at a high temperature ; microlitic and 
spherulitic crystallisation took place in the ex- 
tremely dense base. Pseudotachylyte differs from 
flinty crush-rock (q.v.) in its intrusive habit, and 
in the absence of any structures referable to local 
crushing. (Parijs, Orange Free State.) 

S. J. Shand : Q./.G.S., Ixxii, 1916-17, p. 198. 


PteifOpod Ooze, Murray, 1873. A calcareous deep- 
sea deposit characterised by an abundance of 
pteropod remains. 

J. Murray & A. F. Renard : " Challenger'- Ref. (Deep Sea 
Deposits), 1891, p. 223. 

Ptygmatic Folding, ScJerholm, 1907. -- A term pro- 
posed for the primary folding in migmatites (injec- 
tion gneisses, etc.), caused by the processes to 
which the migmatites owe their origin and com- 
posite character. 

J. J. Sederholm : Bull. Co/urn. Geol. Fiulande, No. 23. 1907, 
p. no. 

Puddingstone. -- A popular term for conglomerates, 
consisting of well-rounded pebbles set in an abun- 
dant matrix. The Hertfordshire Puddingstone, to 
which the name is most commonly applied, is a 
local facies of the Reading- Pebble-beds, which has 
been cemented into a hard siliceous flint-con- 
G. Barrow : Proc. Geol. Assoc., xxx, 1919, p. 5. 

Puglianite, Lacroix, 1917. A phanerocrystalline rock 
composed essentially of augite, leucite, and anor- 
thite. (Mte. Somma.) 

A. Lacroix : C.R., clxv, 1917, p. 210. 

Pulaskite, Williams, 1890. A porphyritic nepheline- 
syenite containing soda-orthoclase, with aegirine- 
augite, barkevikite, and biotite as its characteris- 
tic mafic minerals/ (Pulaski Co., Arkansas.) 

Pumice. A general term applied to lavas so extreme'} 
vesiculated as to resemble froth. Varieties of 
rhyolitic composition are generally light-coloured 
and characterised by a sub-pearly lustre. 

PumiceOUS Structure. A structure akin to that of a 
coarse froth, due to the extreme vest culat ion of a 

lava by expanding gases and vapours. 

Pyribole, Joliannsen, 1911. A general term for mine- 
rals belonging to either the pyroxene or arnphibolc 
groups, suggested for field use. 


PyroclastS. A general term for fragmental deposits 
of volcanic ejectamenta, including volcanic con- 
glomerates, agglomerates, tuffs, and ashes. 
L. V. Pirsson : Am. Journ. Sci., xl, 1915, p. 191. 
J. F. N. Green : Proc. Geol. Assoc., xxx, 1919, p. 153. 

Pyrogenetic Minerals. A term applied to the primary 
magmatic minerals of igneous rocks, excluding 
those due to pneumatolytic, hydrothermal, and 
thermodynamic processes. In practice many cases 
of doubtful character arise, since the solidification 
of a magma may constitute 'a continuous process 
beginning with indubitable pyrogenetic minerals, 
and yet finishing with a well-defined hydrothermal 
series of minerals. 

Pyromeride, Montetro, 1814. A quartz-felsite or 
devitrified rhyolite characterised by conspicuous 
spherulitic or lithophysal structure, and thus hav- 
ing a nodular appearance. 
J. Parkinson : Q.J.G.S., liv, 1898, p. ioi. 

Pyroxenite, Coquand, 1857. - - A general term for 
phanerocrystalline rocks consisting predominantly 
of pyroxenes. Both quartz- and olivine-bearing 
varieties are recognised, and those containing 
segirine-augite or traces of felspathoid are referred 
to as alkali-pyroxenite. Although the above usage 
is now customary in English-speaking countries, it 
should be noticed that in France the term pyro- 
xenite is given to melanocratic facies of pyroxene 

Pyroxenolite, Lacroix, 1894. - - A general term for 
phanerocrystalline rocks of igneous origin, consist- 
ing predominantly of pyroxenes ; pyroxenite 
(French usage) being restricted to metamorphic 
rocks of the same mineral composition. 



Quartz-barytes Rock, Holland, 1897. A rock com- 
posed of about 30 per cent, barytes and 70 per 
cent, quartz, and considered to be of magmatic ori- 
gin, occurring in the Salem district of Madras as 
a network of pegmatite-like veins. 
T. H. Holland : Rec. Geol. Surv. India, xxx, 1897, p. 236. 

Quartz-dlorite. -- A phanerocrystalline igneous rock 
composed of quartz, plagioclase (averaging oligo- 
clase or andesine), hornblende, and generally 
biotite. If orthoclase be present in addition, but 
in amount inferior to that of the plagioclase, the 
rock is then described as granodiorite. Cf. 

Quartz-dolerite. An oversaturated variety of dolerite 
containing interstitial quartz. The latter mineral 
is frequently associated with orthoclase in micro- 
pegmatite, and when this is present the rock is 
described as grano dolerite. 

Mem. Geol. Surv. (Glasgow District), 1911, pp. 118 and 146. 
G. W. Tyrrell : Geol. Mag. 1909, p. 299. 

Quartz-felsitC. A rhyolite or quartz-porphyry having 
a cryptocrystalline or devitrified groundmass ; in 
the older usage of the name it was synonymous 
with quartz-porphyry, but the latter term is now 
more commonly used, especially when conspicuous 
phenocrysts are present. 

Quartzite. A granulose metamorphic rock, represent- 
ing a recrystallised sandstone, consisting pre- 
dominantly of quartz. The name is also used for 
sandstones and grits cemented by silica which 
has grown in optical continuity around each frag- 

W. J. Sollas : Set. Proc. Roy. Dublin Soc., vii, 1892, p. 169. 
L. Cayeux : Structure et Origine des Gres du Tertiare 
farisien, Paris, 1907. 

Quartz-porphyry. A rock containing phenocrysts of 
quartz and alkali-felspar, typically orthoclase, with 
or without mica, in a cryptocrystalline or micro- 


crystalline groundmass. If phenocrysts are abun- 
dant the rock becomes granite-porphyry, while if 
they are absent or inconspicuous, the terms quartz- 
felsite and microgranite are used according to the 
nature of the groundmass. 
J. Morrison : Q.J.G.S., Ixxiv, 1918-19, p. 116. 

Quartz-schist. A schist in which the foliation is due 
to the presence of streaks and lenticles of non- 
granular quartz. Mica is usually present, but in 
less amount than in mica-schist. 

Queluzite, Derby, 1901. A manganese-garnet (spes- 
sartite) rock, in some varieties containing amphi- 
boles, pyroxenes or micas, with or without free 
manganese-oxides. Residual deposits derived 
from this rock constitute valuable manganese-ores. 
(Queluz, Minas Geraes, Brazil.) 

O. A. Derby: Am. Journ. Sci., xii, 1901, p. 18; xxv, 1908. 
P- 213. 


Radio-activity. --An atomic property of certain ele- 
ments belonging to the uranium and thorium 
families, whereby they spontaneously disintegrate 
with external emission of energy, carried in the form 
of a- particles (positively charged helium atoms) or 
^-particles (electrons), into elements of lower in- 
trinsic energy, and, where a-particles are lost, of 
lower atomic weight. Owing to the distribution of 
radioactive elements in the earth's crust, radio- 
thermal phenomena are of critical importance in 
air geological processes in which heat is an active 

A. Holmes : Science Progress, No. 33, 1914, p. 12. 
Geol. Mag,, 1915, pp. 60, 102 ; 1916, p. 265. 

Proc. Geol. Assoc., xxvi, 1915, p. 289. 

Q.J.G.S., Ixxiv, 1918-19, pp. 63, 84. 

Radio-haloes, Hirschi, 1920. See Pleochroic Haloes. 


Radiolarian Ooze, Munay, 1873. A variety of red 
clay (q.v.) characterised by an abundance of the 
siliceous skeletons of radiolaria and of certain 

J. Murray & A. F. Kenard : " Challenger" Rep. (Deep Sea 
Deposits), 1891, p. 203. 

Raglanite, Adams -> Barlow, 1910. A facies of 
nepheline-syenite containing in order of abundance, 
oligoclase, nepheline, and corundum, with small 
quantities of micas, calcite, magnetite, and apatite. 


F. D. Adams & A. E. Barlow : GeoL Surv. Canada Mem. 6 
(Pub. No. 1082), 1910, p. 314. 

Randannite, Salvetat. A local variety of diatomace- 
ous earth occurring in the neighbourhood of the 
Puy-de-D6me. (Randanne.) 

Rang, C.I.P.W., 1902. A division of igneous rocks 
considered after the division into orders, based (in 
classes I., II. and III.) on the relative proportions 
of the molecules of salic K 2 O and Na 2 O to those 
of salic CaO. This division is analogous to the 
more general division of rocks into alkali- and cdlc- 
alkali types, and usually fails to express the kind 
of felspar present. In classes IV. and V. the 
rangs are based on the relative proportions of the 
molecules of MgO,FeO, and femic CaO to those 
of femic K 2 O and Na. 2 O. This is analogous to the 
division of perknites, peridotites and similar rocks 
into normal and alkali-types. 

Rapakivi, Sederholm, 1891. A hornblende-biotite 
granite containing large rounded crystals of ortho- 
clase mantled with oligoclase. The same term 
has also been applied to the youngest pre-Cam- 
brian granites of the Christiania District. 

Ratio of Absorption. The ratio, A, expressed as a 
percentage of the volume V p of the pore-space in 
a rock to the weight W of the rock when dry. 

A = 100 V P /W. 

A. Holmes : 7 'he Geological and Physical Characters of 
Concrete Aggregates, B.F.P.C. Red Book, 256, 1920, p. 


Reaction Rim. A term applied to a peripheral zone 
of mineral aggregates formed around one mineral 
(e.g., hypersthene), by reaction with another (e.g., 
plagioclase), with which it would otherwise come 
into contact. Cf. Kelyphitic; Corona. 
T. H. Holland : Mem. Geol. Surv. India, xxix, 1896, p. 20. 

Red Clay. A widespread deep-sea deposit consisting 
of ferruginous clayey alteration products of vol- 
canic debris, wind-borne particles from desert 
regions, zeolite crystals, concretionary manganese 
and iron oxides, meteoritic matter, and a variable 
content of siliceous or calcareous remains. Where 
the depth is great organic remains may be entirely 
absent owing to the solvent action of sea-water 
which overtakes them as they sink towards the 
ocean floor. At suitable depths and beneath a 
suitable environment the red clay passes laterally 
into globigerina ooze, radiolarian ooze, or diatom 
ooze, all of which have an inorganic residue 
resembling red clay. 

J. Murray & A. F. Renard : " Challenger " Rep. (Deep Sea 
Deposits), 1891, p. 190. 

Red Mud.- A reddish-brown terrigenous deep-sea mud 
which accumulates on the sea-floor in the neigh- 
bourhood of deserts and off the mouths of great 
rivers ; contains CaCO 3 up to 25 per cent. 
J. Murray : " Challenger " Re-p, (Deep Sea Deposits), 1891, 
P- 234. 

Refractories or Refractory Materials. - - Materials 

which will withstand with at least some degree of 
success the effects of the heat and chemical re- 
actions involved in metallurgical and other high- 
temperature processes. They are classified as 
Acid e.g., fireclay, ganister, and sand; 
Neutral e.g., chromite and graphite; and 
Basic e.g., bauxite and magnesite. 

R. Iladneld : Trans. Faraday Soc., xi, 1916. 

P. ('. H. Boswell : British Resources of Refractory Sands, 
Pt. i, 1918. 

Mem. Geol. Surv., Spec. Rep. Min. Resources, vi, 1918. 

T. Crook : Trans. Ceramic Soc., 1919, p. 67. 


Regional Metamorphism, Daubree, 1860. A general 
term for metamorphism due to the sum of the pro- 
cesses which have affected the rocks over exten- 
sive areas ; contrasted with local metamorphism in 
which each area affected is restricted to an aureole 
of limited extent, and related to a definite 
intrusion of magma. Originally the term covered 
changes due to deep burial and the action of heat 
and hot gases from the interior ; by many writers 
it has been used as synonymous with dynamic 
metamorphism, and by others in the sense defined 
above, but with the proviso that the metamorphism 
is not genetically connected with the intrusion of 
magmas. This specified limitation would often 
be difficult to substantiate, for many of the fea- 
tures of regional metamorphism are not distin- 
guishable from those of local or contact metamor- 
phism, except in uniformity, depth and extent. 

F. D. Adams : Q.J.G.S., Ixiv, 1908, p. 127. 

G. Barrow : Proc. Geol. Assoc., xxiii, 1912, p. 274. 

R. A. Daly : Bull. Geol. Soc. Am., xxviii, 1917, p. 394. 
For other references see under Metamorphism. 

Regolith, Merrill 9 1906. A general term for the super- 
ficial blanket of denudation products which is 
widely distributed over the more mature f< solid " 
rocks. The term includes weathering residues, 
alluvium, and aeolian and glacial deposits. 
G. P. Merrill : Rocks, Rock Weathering, and Soils, 1906, 
p. 287. 

Resorption. - - The partial or complete solution by a 
magma of a mineral, or its components, with 
which it is not in equilibrium, or with which, 
owing to changes of temperature, pressure, or 
composition, it has ceased to be in equilibrium, 
The term is often wrongly applied to immature 
crystals, and to crystals which have decomposition 
borders through change of pressure or otherwise. 
O. Andersen : Am. Journ. Sci., xxxix, 1915, p. 451. 


Resurgent, Daly, 1908. A term applied to magmatic 
emanations derived not from the magma itself 
(juvenile), but from entrapped country rock. 
R. A. Daly : Econ. Geol., xii, 1917, p. 491. 

Rhomb-porphvry, or Rhombenporphyr, v. Buch.A 
variety of alkali - syenite - porphyry containing- 
phenocrysts of anorthoclase or potash-oligoclase 
(rhomb-shaped in section), small augites and occa- 
sionally olivine, in a fine-drained groundmass con- 
sisting- mainly of alknli-felspars ; Kenyte (in 
P. Quensel : Bull. Geol. 7ns/. U-psala, xvi, 1918, p. i. 

Rhyobasalt. Shand, 1017. - - A term suggested for 
rocks which are the effusive equivalent of grano- 
dolerite (q.v.). 

Rhyocrvstal, Wright, 1902. A term applied to 
crystals of idiomorphic outline which are arranged 
in stream-lines. 

A. C. Lane : Bull. Geol. Soc. Am., xiv, 1002, p. ?86. 
Rhyolite, v. Richthofen, 1861. A volcanic rock cor- 
responding in chemical composition to granite, 
and generally having small phenocrysts of quartz 
and othoclase (or other alkali-felspar) in a glassy 
or cryptocrystalline groundmass. Flow structure 
is commonly developed, and spherulitic, nodular, 
and lithophysal structures are exhibited by many 

J. P. Tddings : U.S.G.S., jth Ann. Re<p. (1885-6), 1888, p. 255 
(Yellowstone Park). 

A. Harker : Bala Volcanic Series, 1889, p. 9 (N. Wales). 

H. Backstrom : Geol. For en i Stockholm Fork, xiii, 1891, 
p. 637 (Iceland). 

G. A. J. Cole : Sci. Trans. Roy. Dublin Soc., vi, 1896, p. 
77 (Antrim). 

J. P. Iddings : U.S.G.S., Mon. xxxii (ii), 1899, p. 356 
(Yellowstone Park). 

W. S. Boulton : Q.J.G.S., Ix, 1904, p. 450 (Pontesford Hill). 

H. H. Robinson : U.S.G.S., Prof. Pa-p., 76, 1913, p. 103 

Riecke's Principle. A thermodynamic principle which 
states that, since the vapour pressure of a sub- 


stance is increased by external pressure, solution 
(e.g., of a mineral) tends to take place most readily 
at points where the pressure is greatest, and re- 
crystallisation where the pressure is least. 

Rigidity. - - The property possessed by solid bodies 
whereby they offer an elastic resistance to deforma- 
tion. See Elasticity of Form. 

Rigid Solution, Iddings, 1913. -- A term applied to 
rock-gflass to connote its physical state, in contra- 
distinction to a solid solution which implies a 
crystalline condition. 

Ring-dyke. A dyke which follows the course of an 
irregular ring-like fault, and of which the outcrops 
approximate to a closed curve more or less broken 
according to the conditions favouring exposure. 

Geol. Surv. Summ. Prog. (1914), 191^, p. 36. 

E. B. Bailey : Geol. Mag., 1919, p. 466. 

Ripple-mark. An undulating- surface-form produced 
by waves or currents of air or water at their con- 
tacts with unconsolidated sediments, the surface 
being thrown into a series of alternating ridges 
and furrows, which trend at right-angles or 
obliquely to the direction of the flow of the moving- 
fluid, and which, hvdrodynamically, represent sur- 
faces of minimum friction. 

E. M. Kindle : Geol. Surv. Canada, Museum Bull., 25, 1917. 

W. H. Bucher : Am. Journ. Sci., xlvii, 1919, pp. 149 and 241. 

Ripple-mark Index, Kindle, 1917. The ratio of wave- 
length (horizontal distance from crest to crest, or 
from trough to trough) to twice the amplitude (ver- 
tical distance from trough to crest). For ripple 
marks due to water currents the ratio varies from 
20 to 30, whereas for those due to air currents 
(wind) the ratio varies from 3 to 6. The index, 
therefore, provides a criterion of the origin of the 
ripple mark. 
E. M. Kindle : Gee.. Surv. Canada, Museum BnU,, 2$, 1917, 

p. 12. 


RlZZOnite, Doelter, 1903. A term applied to a local 
variety of limburgitc. (Mt. Rizzoni, Tyrol.) 

C. Doelter : Am. Akad. Wisch. Wien, xl, 1903, p. 10. 

Rock. As a geological concept, rock may be defined 
as (a) any formation of natural origin that con- 
stitutes an integral part of the lithosphere, and that 
cannot be referred to a single fossil, or to a single 
individual of a mineral species ; or (b) a representa- 
tive specimen of such a formation. 

" It is as the architectural elements of the earth's 
crust, rather than as aggregates of minerals or 
chemical constituents, that rocks are best and most 
fundamentally considered ; and, unlike a mineral, 
a rock has no scientific significance except in so 
far as it can be regarded as representative of the 
massi from which it has been detached." T. 
Crook : Min. Mag., xvii, 1913, p. 65. 

Rockallite, Judd, 1897. - - A fine-grained mesocratic 
soda-granite, consisting" of aBgirine-acmite, quartz, 
and albite. (Rockall, N. Atlantic.) 

H. S. Washington : Q.J.G.S., Ixx, 1914, p. 294. 

Rock-flour. -- A general term for finely comminuted 
rock-material corresponding in grade to mud, but 
formed by the grinding- action of glaciers and ice- 
sheets, and therefore composed largely of un- 
weathered mineral particles. 

Rock-series, Brogger, 1904. -- An assemblage of jg- 
neous rock types irn a single district and belonging- 
to a single period of igneous activity, charac- 
terised by a certain community of characters, 
chemical, mineral, and sometimes even textural. 
A. Harker : Journ. Geol., viii, 1900, p. 389. 

Rodding Structure. See Mullion Structure. 
Rodingite, Bell, 1911. A coarse-grained gabbro-like 
rock associated with dunite, containing dialla.o-e 
and grossularite. Altered! varieties containing 
prehnite and/or serpentine are recognised. 

(Nelson, New Zealand.) 
J. M. "Bell : Ceol. Sitrv. New Zealand, Bull.. 12, 1911. p. 31. 


Rodite. A brecciated achondritic meteorite composed 
of bronzite and ollvine with small amounts of 
olig-oclase and iron rich in nickel ; = Brecciated 

Rohrbach Solution. -- A yellow aqueous solution of 
barium mercuric iodide, having- a maximum 
specific gravity of 3.^5. 

Rosiwal's MicrometriC Method. A method of deter- 
mining- the percentages (by volume) of the minerals 
in a rock, bv measuring- with an eve-piece micro- 
meter the linear intercepts of each mineral, as seen 
in thin section along- a series of lines suitably dis- 
tributed over the section. The principle of the 
method was originally suggested by Delesse in 

F. C. Lincoln & H. L. Rietz : Econ. Geol., viii, 1913, p. 120. 
S. T. Shand : Jonrn. G"ol., xxiv, 1016, p. ?q4. 
A. Johannsen & E. A. Stephenson : Journ. Geol., xxvii, iqiq, 

P. 212. 

Rougernontite. O'Neill. 1014. A phanerocrvstalline 
rock containing- anorthite and titanaug-ite, with 
small amounts of olivine and iron-ores. 

(Roug-emont, Montreal.) 

J. J. O'Neill : Geol. Sur-v. Canada Mem., 43, (Pub. No. 
1311)1 iQi4. P- 74- 

Routivarite, Sjogren, 1893. A fine-grained ig-neous 
rock composed of orthoclase, plag-ioclase, ouartz, 
and g'arnet. (Routivara, Swedish Lapland.) 

Rouvillite, O'Neill. 1914. -- A leucocratic variety of 
theralite, containing about 53 per cent, of labra- 
dorite, and 27 per cent, of neoheline, with small 
amounts of titanaug-ite, brown hornblende, nvrite 
and aoatite. (St. Hilaire, Montreal.) 

J. J. O'Neill : Geol. Surv. Canada Mem., 43 (Pub. No. 
1311), 1914, p. 35- 

Rubble. A general term for coarse non-graded 

Rudaceous, Grdbau^ 1904, = Psephitic. - - Terms 

applied to sedimentary rocks composed of 
coarsely-graded detritus such as gravel, shingle, 
pebbles, etc. 


Saccharoidal Texture. A granular texture, resemb- 
ling that of loaf-sugar, and typically developed in 
certain statuary marbles. 

Sagvaildite, Rosenbusch, 1883. -- A granuiose meta- 
morphic rock composed essentially of pyroxene and 

Salic, C.l.P. \V ., 1906. A mnemonic term (recalling 
silica and a/umina) applied to the group of stan- 
dard normative minerals which includes quartz, 
felspars and ^elspathoids. 

Saltation, McGee, 1908. A mode of transportation of 
debris by running water, in which the particles 
make intermittent leaps from the bed of the 
stream ; a form of movement intermediate between 
rolling or sliding, and suspension. 
G. K. Gilbert : U.S.G.S. Prof. Pa-p., 86, 1914, p. 15. 

Sandstone. A cemented or otherwise compacted de- 
trital sediment composed predominantly of quartz 
grains, the grades of the latter being those of 
sand. Mineralogical varieties such as lelspathic 
and glauconitic sandstones are recognised, and 
also argillaceous, siliceous, calcareous, ferruginous 
and other varieties according to the nature of the 
binding or cementing material. Corresponding 
rocks composed of coarser grades have been called 
grits, but the same term has also been used to con- 
note angularity of grain, independently of grade- 

L. Cayeux : Structure et Origine des Gres du T ertiare 
parisien, Paris, 1907. 

A. Holmes : British Fire Prevention Committee, Red Book, 
256, 1920, p. 76. 

Sandstone Dykes. A term applied to dyke-like masses 
of sandstone formed by deposition in fissures from 
above or by injection into earthquake-fissures from 

J. S. Diller : Bull. Geol. Soc. Am., i, 1890, p. 411. 


Sanidinite. - - This term has been variously used for 
igneous rocks composed mainly of sanidine or 
other forms of alkali-felspar, whether occurring as 
volcanic, phanerocrystalline, or porphyritic rocks, 
or as ejected blocks, cognate enclosures, or segre- 

A. Lacroix : Enclaves des Roches volcanigues, 1^93 
W. H. Weed & L. V. Pirsson : Am. Journ. Sci., 1, 1893, 
P- 479- 

Santorinite, Washington t 1897. -- A leucocratic vol- 
canic rock, with normative quartz and a high con- 
tent of silica (about 65 per cent.), composed mainly 
of plagioclase varying from labradorite to 
anorthite. The same name has been applied by 
Becke to hypers thene-andesites containing sodic 
andesine or oligoclase, to distinguish such rocks 
from alboranite. (Santorin.) 

Sanukite, Weinschenk, 1890. A volcanic rock of 
andesitic composition, containing crystals of 
hypersthene, garnet, and a little andesine in a 
glassy groundmass ; garnetiferous boninite. 

(San-uka, Japan.) 

Sapropelic Coals, 'Potonie, 1904. A group of coals, 
including the cannel- and boghead-types., which are 
largely composed of the indurated jelly-like slime 
derived from macerated organic debris, and known 
as sapropel. 

Samaite, Brogger, 1883. -- A variety of felspathoid- 
syenite containing cancrinite and aegirine. 

(Sarna, Sweden.) 

Saturated, Shand, 1913. A term applied to minerals 

(e.g., felspars) which are capable of forming in the 

presence of free silica, and extended to describe 

rocks composed wholly of saturated minerals. 

S. J. Shand: Geol. Mag., 1913, p. 508; 1914, p. 485; 1915, 

P- 339- 
A. Holmes : Geol. Mag., 1917, p. 115. 

Saussuritisation. A term applied to processes where- 
by the plagioclase felspars of dolerites and other 
igneous rocks become altered by the breakdown ot 


the solid solution of albite and anorthite into a 
dense aggregate of saussurite. This material, 
originally thought to be a specific mineral, is com- 
posed essentially of albite (or oligoclase) and zoi- 
site (or epidote), together with variable amounts 
of calcite, sericite, and calcium-aluminium silicates 
other than those of the epidote group. The altera- 
tion is specially characteristic of gabbros and green- 
stones (epidiorite and diabase), and is accompanied 
as a rule by uralitisation or chloritisation. It may 
be due to auto-, contact-, or low-grade dynamic- 
G. H. Williams : U.S.G.S. Bull. 62, 1890, p. 67. 

Saxonite, Wads worth, 1884. A peridotite containing 
orthorhombic pyroxene as the essential mineral, in 
addition to olivine; = Harzburgite. 

Scapolite Rocks. A general term for rocks contain- 
ing scapolite irrespective of its origin as a 
major constituent. 

J. E. Spurr : Am. Journ. Sci., x, 1900, p. 310. 
J. S. Flett : Summ. Prog. Geol. Surv. (1906), 1907, p. 116. 
W. G. Foye : Econ. Geol., xi, 1916, p. 677. 
A. Lacroix : Bull. Soc. franf. Min., 1916, p. 74. 

Scapolitisatiotl. The processes whereby the alumino- 
silicate minerals of igneous rocks such as gabbro 
are replaced by scapolite. Plagioclase is the 
mineral commonly so altered, associated augite 
being changed concomitantly to hornblende. 

Schalstein, Stifjt, 1825. A term for altered basaltic 
and spilitic rocks and tuffs; shearing structures 
(incipient schistosity and cleavage), and partial re- 
placement of the rocks by calcite being characteris- 
tic features, 

Schillerisation, ]udd, 1885. The development, along 
certain planes within a mineral, of minute in- 
clusions which reflect light simultaneously and so 
give rise to the appearance known as " schiller. " 
J. W. Judd : Q.J.G.S., xli, 1885, p. 383. 

Schist. -- A general term for foliated metamorphic 
rocks, the structures of which are controlled by 


the prevalence uf lamellar minerals such as micas, 
chlorite, talc, and hornblende (in part), which have 
normally a flaky or elongated habit ; or of stressed 
minerals such as quartz and calcite, which have 
crystallised in elongated forms rather than in the 
granular forms generally assumed in the absence 
of shear. A common characteristic of schists is 
that they may be divided into folia? which are 
mineralogically similar ; whereas in gneisses, alter- 
nating bands or foliae are usually mineralogically 
dissimilar, and the tendency to split is much less 
marked. Cf. Foliation. 
For References, see under Metamorphism. 

Schistosity. The property of a foliated rock whereby 
it can be divided into thin flakes or lenticles, the 
property depending on the parallelism of the cleav- 
age-planes of the lamellar minerals, such as biotite, 
to which the foliation is due. 

Schlieren. An old mining term applied to irregular 
masses, generally streaky in form, occurring in a 
body of igneous rock, from the normal type of 
which they differ transitionally in texture and /or 
composition. They may represent differentiation 
in situ, partial assimilation of fragments of coun- 
try rock, or injections of residual liquors into al- 
ready crystallised material. 

Schonfelsite, Uhlemann, 1909. A variety of picrite- 
porphyry containing phenocrysts of olivine and 
augite in an aphanitic groundmass composed of 
apatite, titaniferous magnetite, bronzite, and 
bytownite, in an interstitial base of brown glass 
and chloride minerals. 

(Altschonfels, Saxony.) 
Uhlemann : Tscherm. Mitt. Pet, Min., xxviii, 1909, p. 434. 

Schorl Rock,- Boase, 1832. A Cornish term for a rock 
composed essentially of aggregates of black tour- 
maline (i.e., of schorl) associated with quartz. 

Schriesheimite, Salomon, 1904. A variety of horn- 
blende-picrite. (Schriesheim, Odenwald.) 


Scoptllite. A variety of crystallite consisting- of rods 
or stems terminated by divergent brushes or 
plumes, characteristic examples of which are found 
in the Corriegills pitchstone of Arraii. 
F. Rutley : Min. Mag., ix, 1891, p. 261. 
Scorise. Lig"ht cellular masses of volcanic rock 

resembling' clinkers. 

Scyelite, ]udd, 1885. A hornblende-biotite-peridotite 
with well-marked poikilitic texture (lustre mottling) 
due to the inclusion of rounded olivines in large 
crystals of other minerals. 

(Loch Scye, Caithness.) 
J. W. Judd : Q.J.G.S., xli, 1885, p. 401. 

Sebastianite, Lacroix, 1917. - - A phanerocrystalline 
rock composed of anorthite and biotite, with 
smaller amounts of augute and apatite. The type 
differs from puglianite, of which it is a hetero- 
morphic form, in containing biotite instead of 
leucite. (Mte. Somma.) 

A. Lacroix : C.R., clxv, iqiy, p. 210. 

Secondary. - - A general term applied to epiclastic 
rocks, and to minerals formed as a consequence of 
the alteration of pre-existing- minerals. Secondary 
minerals may thus be formed in situ as pseudo- 
morphs or paramorphs, or they may be deposited 
from solution in the interstices of a rock through 
which the solution is percolating. It has been 
proposed to apply the terms deuteric or paulopost 
(q.v.} to alterations and alteration products effected 
bv processes genetically associated with those by 
which the primary mineral was formed ; restricting 
secondary to alterations and alteration products 
effected by later processes independent of those 
concerned with the genesis of the primary mineral. 
For example, tourmalinisation is a paulopost pro- 
cess, while lateritisation is a secondary process. 

Secretions. A general term applied to all materials 
which have been deposited from solution bv infil- 
tration in the cavities of rocks, e.g. , amygdales. 
geo&es. Cf. Concretions. 


Sedimentary Rocks. A general term for loose and 
cemented sediments of detrital origin, generally 
extended to include all exogenetic rocks (residual, 
detrital, organic, and solution deposits). Cf. 

E. Andree : Geol. Rnnd., ii, 1911, pp. 61, 119. 

A. C. Trowbridge : Journ. Geol., xxii, 1914, p. 420. 

G. M. Davies : Proc. and Trans. Croydon Nat. Jlist. a>:cl 
Sci. Soc., 19115-16, p. 153. 

P. G. H. Boswell : Geol. Ma?., xxvii, 1916, pp. 105, 163. 

L. Cayeux : TJ Etude pe'trogra-phique des Roches sedi- 
mentaires; Mem. Carte Geol. France. 1916. 

E. M. Kindle : Journ. Geol., xxvii, 1910. p. -^9. 

W. Deeke : Ber. Naturfor. Gesell., xxii, (i), 1910. 

Seebenite, Salomon, i8q8. A variety of hornfels con- 
taining felspar and cordierite as the dominant 
minerals. (Seeben, near Klausen.) 

Segregations. A term applied to authigenous mineral 
aggregates, in masses or streaks, occurring in 
igneous rocks, and representing earlv products of 
crystallisation from the same respective magmas ; 
= Endogenous enclosures = Cognate inclusions. 

Selagite, Cordier, 1868. A variety of mica-trachyte, or 
minette, characterised by abundant phenocrvsts of 
bleached bietite in al groundmass of orthoclaF-e 
and oligoclase laths with grains of diopside. 
II. S. Washington: Am. Journ. Sci., ix, io<~~o, p. 47. 

Septarian Structure. A structure developed in cer- 
tain concretions known as septarian nodules, due 
to an irregular polygonal system of internal 
cracks, which are almost always occupied bv cal- 
cite or other minerals. The structure closely re- 
sembles the desiccation-structure of mud-cracks, 
and is probably developed bv a similar cause 
contraction due to the desiccation of the colloidal 
material in the interior. 
W. A. Richardson : Mln. Mag., xviii, 1919, p. 127. 

Seriate Fabric, C.J.P.W., 1906. A variety of inequi- 
granular texture, in which the sizes of the crystals 
form a continuously graded series. 
J. P. Iddings : Igneous Rocks. I, 1909, p. 196. 


Serialisation. The hydrothermal or other processes 
whereby alumino-silicate minerals are replaced by 
W. Lindgren : .Trans. Am. Inst. Min. Rng., xxx, 1900, p. 

609. * 

Series. A term applied to a number of related rocks 
or minerals arranged, or capable of arrangement, 
in a natural sequence of succession, composition 
or other property; e.g., Charnockite Series, Pyro- 
xene Series. Stratigraphically the term is applied 
to the main subdivisions of Systems. 
Serpentine. A rock made up predominantly of ser- 
pentine ; generally formed by the hydrothermal 
alteration of neridotites. 
T. G. Bonney : Q.J.G.S., xxxiii, 1877, p. 884; Ixiv, 1908, 

p. 152. 

J. S. Flett : Mem. Geol. Surv., 359 (Lizard), 1912, p. 61. 
R. P. D. Graham : Econ. Geol. xii, 1917, p. 154. 
W. N. Benson: Am. Journ. Sci., xlvi, 1918, p. 693. 
Serpentinisation. The process whereby magnesium- 
rich minerals and rocks are altered to serpentine. 
Shackanite, Daly, 1912. A variety of analcite- 

(Shackan, Midway Range, British Columbia.) 
R. A. Daly : Geol. Surv. Canada, Mem., 38 (Pub. 1203), 

1912, p. 414. 

Shale. - - A laminated sediment, in which the con- 
stituent particles are predominantly of the clay 
W. M. Hatchings: Geol. Mag., 1894, pp. 36, 64; 1896, pp. 

39> 343- 

Shastaite, Iddings, 1913. A general name suggested 
for andesine-dacites, i.e., for normal dacites. 

(Mt. Shasta, California.) 

Shastalite, Wadsivorth, 1891. A term suggested for 
unaltered andesite-glass. 

(Mt. Shasta, California.) 

Sherghottite. An achondritic meteorite mainly com- 
posed of augite and maskelynite. 

Shimmer-aggregate, Barrow, 1893. A micaceous 
aggregate replacing altered alumino-silicate 


minerals such as kyanite and cordierite in meta- 
morphic rocks. 
G. Barrow : Q.J.G.S., xlix, 1893, p. 340. 

Shingle. Loose detritus of coarser grades than those 
of gravel, e.g. , having- a majority of the pebbles of 
larger size than a walnut. 

Shonkinite, Pirsson, 1895. A melanocratic and gener- 
ally felspathoidal syenite or monzonite composed of 
orthoclase, plagioclas<e and pyroxene, with a small 
and variable amount of nepheline. 

(Shonkin Sag, Montana.) 
W. H. Weed & L. V. Pirsson : Bull. Geol. Soc. Am., 6, 

1895, P- 4i5- 
G. W. Tyrrell : Trans. Roy. Soc. Edin., li, 1915, p. 552. 

Shoshonite, Iddings, 1895. A mafic variety of olivine- 
trachydolerite, containing orthoclase-mantled 
labradorite ; associated with absarokite and 
banakite. (Shoshone R.. Yellowstone Park.) 

J. P. Iddings : Journ. Geol., iii, 1895, p. 943. 
- U.S.G.S., Mon. xxxii (ii), 1899, p. 339. 

Siderite. -- A general term for meteoric irons, com- 
posed almost wholly of nickel-iron, including 
hexahedrites, octahedrites, and ataxites. 

Siderolite, Maskelyne, 1863. - - A genera] term for 
stony-iron meteorites which contain large propor- 
tions of both silicates and nickel-iron. The silicate 
minerals include bronzite and olivine, and, in small 
amount, anorthite. Brezina has restricted the 
term to include onlv the mesosiderites, lodranite, 
and graham ite. Cf. Lilhosiderite. 

Siderophyre, Tschermak, 1883. A siderolite contain- 
ing crystals of bronzite and asmanite (tridymite) in 
a network of nickel-iron. 

Sieve Texture. A texture of metamorphic rocks due 
to the occurrence of abundant inclusions in larger 
spongv crystals ; = Diablastic. 

Silcrete. Lamplugh, TQ02. - - A term suggested for 
conglomerates formed bv the cementation of 
superficial travels bv silica. 
G. W. Larrmlugri : Geol. Mag.. 1902, p*. 575. 

Silex. = Flint. 


Silexite, Miller, 1919. A term proposed for any body 
of pure or nearly pure silica of igneous or aqueo- 
igneous orig-in, which occurs as a dyke, segrega- 
tion mass, or cognate inclusion. 
W. J. Miller : Journ. Geol., xxvii, 1919, p. 30. 

Siliceous Sinter. A solution-deposit of silica formed 
from the waters of geysers and other thermal 
W. H. Weed : U.S.G.S. gth Ann. Rep., 1887-8, 1890, p. 619, 

Sill. A tabular sheet of igneous rock injected along 
the bedding planes of sedimentary or volcanic 
formations ; = Intrusive sheet. 

Siltstone, Green. A very fine-grained sandstone, the 
particles of which are predominantly of silt grade. 

Sismondinite, Franchi, 1897.- A schist having sis- 
mondine as its predominant mineral. 

Sivamalai Series, Holland, 1901. A series of igneous 
rocks occurring in Madras, produced by the dif- 
ferentiation of a highly aluminous and alkaline 
magma ; the chief rock tvpes being nepheline-, 
augite-, and corundum-syenites and siliceous peg- 

(Sivamalai, Coimbatore district, Madras.) 
T. H. Holland : Mem. Geol. Surv. India, xxx, iqoi, D. i6q. 

Skarn. An old Swedish mining term for the silicate 
gangue (amphibole, pyroxene, garnet, etc.) of cer- 
tain iron-ore and sulphide deposits of Archaean age, 
particularly those which have replaced limestone 
and dolomite. The term is used in this sense by 
Fennoscandian geologists, but it has been extended 
to cover analogous products of contact meta- 
morphism in younger formations. 
V. Goldschmidt : Die Kontaktmet amor -phase im Kristianiage. 

biet, 1911. 
P. Eskola : Bull. Comm. Geol. Finlande, No. 40, 1914, p. 225 

Sklerooelite, Salomon, 1915. -- A term proposed for 
argillaceous and allied rocks which have been in- 
durated bv low-grade metamorphism. The tvpe is 
more dense and massive than shale, and differs 
from slate in the absence of cleavage. 
W. Salomon : Geol . Rund., vi, 1915, p. 404. 


Skomerite, Thomas, 1911. A volcanic rock, contain- 
ing- phenocrysts of augite and albite-oligoclase, 
with less abundant olivine, in a felted ground- 
mass, consisting- predominantly of albite. 

(Skomer I., Pembroke.) 
H. H. Thomas: Q.J.G.S., Ixvii, 1911, p. 175. 

Slate. A general term for compact aphanitic rocks 
formed from fine-grained deposits such as shales, 
mudstones, or volcanic ashes, having the property 
of easy fissibility along planes independent of the 
original bedding, whereby they can be parted into 
thin plates indistinguishable from one another in 
lithological characters. 

W. M. Hutchings : Geol. Mag., 1890, pp. 264, 316; 1891, 
p. 164; 1892, pp. 154, 218; 1894, pp. 36, 64. 

Soda-. A prefix added to the names of igneous rocks 
to indicate that they contain soda-pvroxenes and/or 
soda-am phi boles ; e-g-> soda-rhyolite, soda- 
trachyte, soda-granite, etc. 

Sodalitite, Ussing, IQIT. A phanerocrystalline rock, 
composed essentially of sodalite, with small 
amounts of aeeirine, eudialvte, and alkali-felspar. 
N. V. Ussing : Mfdd. om Gronland, xxxviii, 1911. 

Soggendalite, Kolderup, 1896. - - A melanocratic 

dolerite rich in pyroxene. 

(Soggendal, Norway.) 
C. F. Kolderup : Bergens Mus. Aarb., 1896, p. 159. 

Sol. A homogeneous suspension of colloidal matter 
in a liquid. See Colloid. 

Solfataric. - - A term applied to a " dormant " or 
"decadent" stage of volcanic activity char- 
acterised by the emission at the surface of gases 
and vapours of volatile substances. 
F. W. Clarke : U.S.G.S. Bull 616 (Data of Geochemistry}, 
1916, p. 260. 

Solid Solution. A crystalline and homogeneous 
solid, representing a mixture of two or more sub- 
stances, and often, though not necessarilv, com- 
posed of isomorphous compounds. The pro- 
portions of such a mixture can change within cer- 
tain critical limits without destroying the homo- 


geneity. Many of the common igneous rock- 
forming minerals are complex solid solutions, 
e.g. , felspars, pyroxenes and amphiboles ; whereas 
minerals formed by the action of shearing stress 
in rocks undergoing metamorphism are generally 
of less complex constitution. 

Solvsbergite, Brogger, 1894. -- A fine-grained hole- 
crystalline rock with trachytic texture, consisting 
of alkali-felspars with soda-pyroxenes and amphi- 
boles. The rock is richer in mafic minerals than 
bostonite and differs from grorudite by the absence 
of quartz. (Solvsberg, Norway.) 

W. C. Brogger : Ern-ptivgest. Kristiania, i, 1894, p. 67. 

Sommaite, Lacroix, iqo$. A monzonitic rock occur- 
ring as ejected blocks, containing bytownite, 
orthoclase, augite and olivine, and occasionally 
in small amount, leucite. Chemically the rock 
corresponds with ottajanite. 

(Mte. Somma, Vesuvius.) 
A. Lacroix : C.R., cxli, TQO^, p. 1188. 

Sondalite, Stache cV von John, 1877. A metamorphic 
rock composed of cordierite, quartz, garnet, tour- 
maline and kyanite. 

vSonstadt Solution. See Thoulet Solution. 

Sordawalite, N&denskjold, 1820. A name given to 
the vitreous selvage of a dyke of olivine-dolerite ; = 
WichtisitSj = Tachylyte. 

(Sorclawala, L. Ladoga, Finland.) 

Soret Principle. A thermo-dynamic principle, stat- 
ing that if the temperature varies from point to 
point in any dilute solution, the concentration of 
the solute also varies, and in such a wav that 
equilibrium is only established when the concen- 
tration is everywhere proportional to the absolute 

Sparagmite. - - A collective term for the late Pre- 
Cambrian or Jotnian Scandinavian rocks, which, 
like those of the Torridonian of Scotland, com- 
prise polygenetic conglomerates, felspathic grits, 
arkose, and graywacke*. 


Specific Gravity. - The ratio of the mass of any 
quantity of a substance to the mass of an equal 
volume of some standard substance. In the case 
of solids and liquids the latter is chosen as water 
at 4 C. Cf. Density. 
A. Holmes : Petrogra-phic Methods and Calculations, 1920. 

Specific Heat. The quantity of heat necessary to raise 
the temperature of one gram of a given substance 
by i C. 
K. Schulz : Fort, der Min. Krist. Pet., ii, 1912, p. 250; 

1913, p. 273. 

W. P. White: Am. Journ. Sci., xlvii, 1919, pp. i, 44. 
Sperone. - - A porous variety of leucitite containing 

small crystals of melanite. 

Spessartjte, Rosenbusch, 1895. A diorite-lamprophyre 
consisting- essentially of green hornblende and 
plagioclase. The name is also used for gfarnets 
which approximate in composition to Mn,AL(SiO 4 ) 8 . 


Sphenolith, Burckhardt, 1906. An injected igneous 
intrusion having an approximately wedge-shaped 

C. Burckhardt : Cong. Geol. Inter. Guide, 26 (Mexico). 1906, 
P- 33- 

Spheroidal. See Orbicular. 

Spheroidal Parting. A structure due to uniform con- 
traction during cooling produced in igneous rocks 
of fine homogeneous grain, and occurring as a 
series of concentric spheroidal or ellipsoidal cracks 
about compact nuclei. Each set of cracks is more 
strong-lv developed during weathering, the succes- 
sive shells so produced resembling- the layers of an 
onion, and varving in diameter from an inch or 
two to several feet. 

Spherulite, Vogelsdng, 1872. A radiating and often 
concentricallv arranged aggregation of one or 
more minerals, in outward form approximating 'to 
a spheroid, and due to the radial growth of pris- 
matic or acicular crystals in a viscous magma 
or rigid glass about a common centre or inclusion. 


The spherulitic body itself is said to have a radial or 
concentric texture, while the rock, which may be 
hemicrystalline, devitrified, or still glassy, is said 
to have a spherulitic structure, 
F. E. Wright : Bull. Geol. Soc. Am., xxvi, 1915, p. 255. 

Spherulitic Structure. A structure in which spheru- 
lites are distributed through an igneous rock or 

W. Cross : Butt. Phil. Soc. Wash., xi, 1891, p. 411. 
J. P. Iddings : Bull. Phil. Soc. Wash., xi, 1891, p. 445. 
L. V. Pirsson : Am. J. Sci., xxx, 1910, p. 97. 

Spiculite, Rutley, 1891. A spindle-shaped crystallite 
considered to represent the coalescence of a linear 
series of globulites ; = Belonite. 
F. Rutley : Min. Mag., ix, 1891, p. 263, 

Spilite, Brongniart, 1827. A basaltic rock, generally 
vesicular or amygdaloidal, whose felspars have 
been albitised. Pyroxene or amphibole, more or 
less altered, and sometimes serpentinised olivine 
may be present. 

Spilitic Suite, Deivey cV Flett, 1911. -- A suite of 
igneous rocks, comprising extrusions and minor 
intrusions, characterised throughout by an abund- 
ance of soda-felspar, and by the prevalence of 
albitisation ; named after spilite, the type member 
of the suite. 

II. Dewey & J. S. Flett : Geol. Mag., 1911, p. 202. 

J. A. Thomson : Q.J.G.S., Ixix, 1913, p. 665. 

A. H. Cox : Rep. Brit. Assoc. (Birmingham, 1913), 1914? P. 

Spilosite, Zincken, 1841. A contact metamorphosed 
shale or slate, having a maculose structure, due to 
the presence of aggregates of cryptocrystalline 
matter rich in iron-oxides, in a streaked matrix of 
sericite and chlorite and minute grains of quartz. 
H. Dewey : Trans. Roy. Geol. Soc. Cornwall, xv, 1915, 
p. 71. 

Spotted Slates or Spotted Schists. In argillaceous 
rocks, altered by contact metamorphism of low to 
moderate intensity, metamorphic diffusion and dif- 


ferentiation about numerous centres effect partial 
reconstitution convergent towards, but not neces- 
sarily attaining to definite minerals. Arrested 
development may be recorded in concretionary 
spots of imperfectly individualised minerals (such 
as andalusite, cordierite, mica or chloritoid) in a 
felted base composed largely of sericitic matter. 
For varieties of such spotted rocks there are no 
special terms in British nomenclature, the follow- 
ing German terms having been widely adopted : 
Fleckschiefer. Characterised by minute flecks 

or spots of indeterminate material. 
Fruchtschiefer. - - Characterised by concre- 
tionary spots suggestive of grains of wheat. 
Garbenschiefer. Characterised by concre- 
tionary spots suggestive of carraway seeds. 
Knotenschiefer. Characterised by conspicuous 
subspherical or polyhedral clots often com- 
' posed of definitely individualised minerals. 
All these types are allied to and pass into ordi- 
nary varieties of hornfels and schist. Cf. 

Stalactite. A pendant concretionary deposit of cal- 
cium carbonate formed from percolating solutions 
in icicle-like masses on the roofs of limestone 
caverns and in other analogous situations. 
Stalagmite. A concretionary deposit of calcium car- 
bonate formed from dripping solutions on the 
floors and walls of limestone caverns, and in other 
analogous situations. 

Static Metamorphism, Judd, 1889. - - A variety of 

regional metamorphism brought about by the 
action of heat and solvents, at high pressures, the 
latter being due to a superincumbent load, and not 
induced by erogenic deformation. 
R. A. Daly : Bull. Geol. Soc. Am., 23, 1917, p. 397. 
Staurotile, Cordier, 1868. -- A variety of mica-schist 
characterised by porphyroblastic crystals of stauro- 
lite, often accompanied by garnet. 


StOCkwork. A mineral deposit, consisting of a sys- 
tem of small reticulated veins (forming a com- 
plicated network) traversing the country rock. 

Strain-shadows. A general term for the undulatory 
extinction seen in homogeneous minerals, such as 
quartz, indicating a modification of the normal 
optical properties due to strain. The phenomenon 
is commonly seen in cataclastic rocks, and must 
not be confused with the partial extinction of zoned 

Strain-slip Cleavage. A variety of cleavage occur- 
ring in certain low-grade metamorphic rocks, due 
to differential movement or " slip " along each of a 
nearly parallel series of closely-packed shear- 
planes. Between each pair of shear-planes the 
rocks are puckered into sigmoidal microscopic 
folds, the outer limbs of which merge tangentially 
into the shear-planes. 
T. G. Bonney : Q.J.G.S., xlii, 1886, p. 95. 

Streaky Structure. A term denoting the presence in 
rhyolitic and allied rocks of numerous dark films or 
lenticular veinlets, arranged parallel, or nearly so, 
to the flow-surfaces, and containing minerals such 
as quartz, pyrite, chlorite, sericite, carbonates, 
e pi dote, and sometimes garnet. Typically 
developed in the Lake District, the " streaks " 
are considered to be due to deposition in and 
around contraction cracks from infiltrating solu- 
tions under high pressure during the solfataric 
stage of the Borrowdale vulcanism. 
J. F. N. Green : Min. Mag., xvii, 1915, p. 207. 

Stress Minerals, Harker, 1918. -- A term suggested 
for minerals such as chlorite, chloritoid, talc, 
albite, epidote, amphiboles, kyanite, etc., whose 
formation in metamorphosed rocks is favoured by 
shearing-stress ; contrasted with anti-stress 
minerals (q.v.). 
A. Harker : Q.J.G.S., Ixxiv, 1918, p. Ixxvii. 

Stromatolithic, Foye, 1916. A term, meaning 
" stone layer," applied, to the banded structure of 


composite gneisses which consist of alternating- 
layers of igneous and schistose rocks in sill rela- 
W. G. Foye : Journ. Geol., xxiv, 1916, p. 783. 

Stronalite. A name given to the cataclastic biotite- 
gneisses associated at Strona with diorite-gneiss 
and kinzigite. (Strona, Ivree, W. Alps.) 

Structure. A term applied (a) to the morphological 
features of rocks due to fracture, e.g., columnar 
structure, perlitic structure ; and (b) to the appear- 
ance of a heterogeneous rock in which the textures 
or composition of neighbouring parts differ from 
one another, e.g. , spherulitic structure, orbicular 
structure, bedded structure, gneissose structure, 
banded structure. 
SEDIMENTS : H. C. Sorby : Q.J.G.S., Ixiv, 1908, p. 171. 

A. C. Trowbridge : Journ. Geol., xxii, 1914, 

p. 420. 

B. Smith : Geol. Mag., 1916, p. 146. 

E. M. Kindle : Geol. Mag., 1916, p. 542. 
IGNEOUS ROCKS : R. B. Sosman : Journ. Geol., xxiv, 1916, 

p. 215. 
F. F. Grout : Journ. Geol., xxvi, 1918, 

P- 439-- 
MKTAMURPHIC ROCKS : U. Grubenmann : Fort, der Min. 

Krist. u. Pet., ii, 1912, p. 208. 

Stubachite, Weinschenk, 1891. An altered diallage- 
peridotite containing tremolite, talc, serpentine, 
magnetite, pyrite and breunnerite in variable 
amounts. By increase of serpentine the type 
passes into stubachite-serpentine. 

(Stubachtale, Tyrol.) 

Stylolites. A term applied to parts of certain lime- 
stones which have a column-like development ; the 
" columns " being generally at right-angles or 
highly inclined to the bedding planes, having 
grooved, sutured or striated sides, and irregular 
cross sections. 
G. H. Gordon : Journ. Geol., xxvi, 1918, p. 561. 

Subhedral. See Hypidiomorphic. 

Sub-rang, C.I.P.W., 1902. A division of rangs 
(q.v.) based (in Classes I., II. and III.) on the 


relative proportions of the molecules of salic K 2 O 
to salic Na 2 O, roughly corresponding to the divi- 
sion of rocks based on the proportions of ortho- 
clase and leucite to those of albite and soda- 
felspathoids. In Classes IV. and V. the sub-rangs 
are based on the relative proportions of MgO to 

Subsilicic, Clarke, 1911. A term suggested in place 
of " basic " to connote that the rocks so described 
have a silica-content leiss than 52 per cent. 

Sudburite, Coleman, 1912. A variety of basalt, often 
amygdaloidal and characterised by pillow struc- 
ture, and in places somewhat sheared and meta- 
morphosed, consisting essentially, when fresh, of 
bytownite, hypersthene, augite and magnetite (15- 
20 per cent.). The type is regarded as the effusive 
equivalent of norite and may be uniformly fine- 
grained or porphyritic. (Sudbury, Ontario.) 
A. P. Coleman : Ontario Bur. Mines, zyd Ann. Re-p., xxiii, 
1914, p. 215. 

Suldenite, Stache & John, 1879. A variety of horn- 
blende-andesite differing from ortlerite in having 
an andesitic rather than a microdioritic ground- 
mass. (Mte. Confinale, Tyrol.) 

Sussexite, Kemp, 1892. A nepheline-porphyry, con- 
sisting essentially of nepheline and/ segirine ; a 
tinguaite-like rock, free from essential felspar. 
Cf. nephelinite and urtite. 

(Sussex Co., New Jersey.) 

Sutured Texture. A texture of granulose meta- 
morphic rocks, in which the individual grains meet 
in irregular interlocking contacts. 

Syenite, Pliny. A term originally applied to horn- 
blende-granite, now connoting a phanerocrystal- 
line rock composed essentially of alkali-felspars, 
and one or more of the common mafic minerals, 
hornblende being especially characteristic. When 
quartz is present the term quartz-syenite is used. 
With increase in soda-lime-felspars relative to 



orthoclase, the rock passes from syenite through 
syenodiorite to diorite, or through monzonite to 
gabbro. The rock of Syene, Egypt, is a red horn- 
blende-granite ; the type syenite is that of Dresden 
(Plane nite). 
H. S. Washington : Am. Journ. Sci., xxii, 1906, p. 132. 

Syenodiorite, 'Evans, 1916. A term based on the form 
of granodiorite for rocks like the latter, but free 
from quartz, i.e., for phanerocrystalline igneous 
rocks intermediate in composition between syenite 
and diorite. Rocks of this, kind have generally 
been called monzonite, a term which should, how- 
ever, be restricted to types intermediate between 
syenite and gabbro. =Monzo diorite. 

Syenogabbro, Johannsen, 1917. A term suggested 
for quartz-free grano gabbro, i.e., for phanero- 
- crystalline igneous rocks intermediate in composi- 
tion between labradorite-monzonite and gabbro. 

Symplektite, Lcewinson-Lessing, 1897. A secondary 
intergrowth of two minerals which are interwoven 
or plaited together, one of the minerals having 
often a vermicular habit. The texture so pro- 
duced is described as symplektitic, and is found in 
certain igneous and thermally-metamorphosed 
J. J. Sederholm : Bull. Comm. Geol. Finlande, No. 48, 1916. 

Synantetic, Sederholm, 1916. A term applied to 

minerals formed between two other minerals 

by interaction between the latter; as in 

coronas, kelyphitic borders, reaction rims, etc. 

J. J. Sederholm : Bull. Comm. Geol. Finlande, No. 48, 1916. 

Syngenetic. A term now generally applied to ore- 
deposits formed contemporaneously with the 
enclosing rocks, contrasting them with epigenetic 
deposits of later origin than the enclosing rocks. 

Syntectic, Lceivinson-Lessing, 1899 A term applied 

to magmas produced by syntexis, and also used 

substantively to connote the magmas themselves. 

R. A. Daly : Igneous Rocks and their Origin, 1914, p. 312. 


Syntexis, Lcewinsqn-Lessing, 1899. The sum of the 
processes whereby mag-mas are generated or aug- 
mented owing to the remelting or assimilation of 
portions of the lithosphere which comprise dif- 
ferent classes of rocks. The term is thus of 
broader scope than anatexis, which implies re- 
fusion of a portion of the crust consisting- pre- 
dominantly of one type 1 of rock, such as granite. 
F. Loewinson-Lessing : GeoL Mag., 1911, p. 297. 

System. A term applied to the sum of the phases that 
can be formed from one, two (binary system), three 
(ternary system), or more components under dif- 
ferent conditions of temperature, pressure and 
composition. Systems, or parts of systems, are 
described, as shown below, in terms of their com- 

Plagioclase, Albite-Anorthite : A. L. Day & E. T. Allen : 
Am. Journ. Sci., xix, 1905, p. 93. 

- N. L. Bowen : Am. Journ. Sci., xxxv, 1913, p. 577. 

Forsterite-Silica : N. L. Bowen & O. Andersen : Am. Journ. 
Sci., xxxvii, 1914, p. 487. 

Diopside- Albite-Anorthite : N. L. Bowen : Am. Journ. Sci., 
xxxviii, 1914, p. 222. 

Anorthite-Forsterite-Silica : O. Andersen : Am. Journ. 
Sci., xxxix, 1915, p. 407. 

Diopside- Albite-Anorthite : N. L. Bowen : Am. Journ. Set., 
xl, 1915, p. 161. 

CaO A1 2 O 3 SiO 2 : G. A. Rankin & F. E. Wright : Am. 
Journ. Sci., xxxix, 1915, p. i. 

General : N. L. Bowen : Journ. GeoL Supp. Vol., xxiii, 

CaO A1 2 O 3 MgO : G. A. Rankin & H. E. Merwin : 

Journ. Am. Cnem. Soc., xxxviii, 1916, p. 568. 
Fe 2 O 3 Fe 3 O 4 : R. B. Bosnian & J. C. Hostetter : Journ. 

Am. Cnem. Soc., xxxviii, 1916, p. 807. 
CaCO 3 : J. Johnston et aliter : Am. Journ. Sci., xli, 1916, 

P- 473- 
Nepheline : NaA.lSiO 4 KAlSiO 4 : N. L. Bowen: Am. 

Journ. Sci., xliii, 1917, p. 115. 
H 2 O K 2 SiO 3 _ SiO 2 : G. W. Morey : Journ. Am. Cnem. 

Soc., xxxix, 1917, p. 1173- 
MgO A1 2 O ? SiO 2 : G. A. Rankin & H. E. Merwin : Am. 

Journ. Sci., xlv, 1918, p. 301. 
CaO MgO SiO 2 : J. B. Ferguson & H. E. Merwin: Am. 

Journ. Sci., xlviii, 1919, p. 165. 


Tachylyte, Breithaupt, 1826. A black compact glassy 
rock of lustrous basaltic composition, generally 
occurring as a chilled selvage in dykes and sills, 
but in Hawaii exceptionally forming the bulk of 
certain lava flows. 

G. A. J. Cole : Q.J.G.S., xliv, 1888, p. 300. 
A. Harker : Mem. Geol. Surv. Scot. (Small Isles), 1908, 
P- 155- 

Taconite. A term used in the Lake Superior district 
for ferruginous cherts of Animikian age. The 
rocks so designated are of various tints, and may 
be finely granular, banded, or brecciated. They 
represent a complete replacement of greenalite- 
rock (q.v.) by silica, iron-ores, and ferruginous 

C. R. Van Hise C. K. Leith : U.S.G.S., Mon. Hi, 1911, pp. 
181, 468. 

Tactite, Hess, 1919. A general term suggested for 
rocks of complex mineral composition formed by 
the contact metamorphism of limestone, dolomite, 
and other carbonate rocks, and into which foreign 
matter from the intrusion has been introduced by 
hot solutions. Rocks of the enclosing zone, such 
as tremolite- and wollasfonite-marbles, are not 
covered by the term. 
F. L. Hess : Am. Journ. Sci., xlviii, 1919, p. 377- 

Tahitite, Lacroix, 1917. A variety of felspathoidal 
trachyandesite containing phenocrysts of hauyne. 
The rock is a microlitic form of the nepheline-mon- 
zonite with which it is associated in the type- 
locality. (Tahiti, Pacific.) 
A. Lacroix : C.R., clxiv, 1917, p. 581. 

Taimyrite, Chrouschoff, 1892. A variety of soda- 
trachyte characterised by the presence of actual or 
occult quartz, and regarded as the effusive equiva- 
lent of nordmarkite. 


Talc-Schist. A schist in which talc, generally asso- 
ciated with mica and quartz, is the dominant 
schistose mineral. 

Tamaraite, Lacroix, 1918. A melanocratic dyke rock, 
containing- augite and barkevikite as the chief 
mafic minerals, and nepheline, or analcite, as the 
chief felsic constituent ; in addition small amounts 
of orthoclase or plagioclase may be present. The 
type is thus a lamprophyric facies of nepheline- 
bas;alt. (Los Archipelago.) 

A. Lacroix : C.R., clxvi, 1918, p. 543. 

Taraspite. A mottled variety of compact dolomite of 
Jurassic age, used for decorative purposes. 

(Tarasp, Switzerland.) 

Taurite, Lagorio, 1897. A soda-rhyolite characterised 
by the presence of aegirine, and differing from 
comendite in having a spherulitic or micro- 
granophyric groundmass. 

(Near Sebastopol, Crimea.) 

Tavolatite, Washington, 1908. A leucite-rich vol- 
canic rock, containing large phenocrysts of leucite 
in a groundmass of leucite, hauyne, and augite 
with small amounts of orthoclase, labradorite and 
garnet. Intermediate between leucitite on the 
one hand, and leucite-trachyte or tephrite on the 
other. (Tavolato, Roman district.) 

H. S. Washington : Carnegie Inst. Wash., Pub. No. 57, 1906, 
p. 50. 

Tawite, Ramsay, 1894. A phanerocrystalline rock 
composed essentially of sodalite and aegirine. With 
the incoming of alkali-felspar the rock passes 
through felspathic - tawite to sodalite-syenite. 
Porphyritic rocks of the same composition are 
known as Tawite-porphyry. (Kola Peninsula.) 

Taxite, Lcewinson-Lessing, 1891. A general term for 
volcanic rocks of clastic appearance owing to the 
consolidation and aggregation of more than one 
kind of product from the same flow. When the 
different consolidation products are disposed in 
alternating bands the resulting rock is described as 


eutaxite, and the structure as eutaxitic. When 
the aggregation resembles a breccia, the rock is 
described as ataxite, and the structure as ataxitic. 
F. LoewinsonrLessing : Bull. Soc. Beige Geol., v, 1891, p. 

Tectonite, Backlund, 1918. A mylonitic rock formed 
from crystalline schists of sedimentary origin and 
in part again recrystallised. Cf. Proiomylonite. 
H. G. Backlund : Geol. For. Fork., xl, 1918, p. 198. 

Tektite, Suess, 1900. A group term suggested for 
moldavites, billitonites, australites, and queen- 
stownites, in place of the term obsidianitc proposed 
by Walcott. 

F. E. Suess : Mitt. Geol. Ges. Wien, vii, 1914, p. 54. 

F. P. Mueller : Geol. Mag., 1915, p. 206. 

Tephrite, Cordier, 1816. A basaltic rock containing 
plagioclase and nepheline or other soda-fels- 
pathoid. With the addition of olivine the rock 
becomes basanite. 

Tephritoid, Bilcking. -- A rock having the chemical 
composition of a tephrite, but containing a soda- 
rich glassy base in place of nepheline. Cf. 

Terra rossa. A red ferruginous earth formed as a 
residual product during the subserial denudation 
of limestones, the type area of its occurrence be- 
ing the Karst lands of the Adriatic. 

Teschenite, Hohenegger, 1861. An alkali-rich variety 
of analcite-dolerite characterised by the presence 
of idiomorphic purple augite or aegirine-augite, 
and generally containing soda-amphiboles such as 
barkevikite. (Teschen, Bohemia.) 

G. W. Tyrrell : Q.J.G.S., Ixxii, 1917, p. 84. 

Mem. Geol. Surv. Scot. (East Lothian), 1910, p. 114. 

Texture. The appearance, megascopic or microscopic, 
seen on a smooth surface of a homogeneous rock 
or mineral aggregate, due to the degree of crystal- 
lisation (crystallinity}, the size of the crystals 


(granularity), and the shapes and interrelations of 
the crystals or other constituents (fabric). 

J. E. Spurr : Journ. Geol., ix, 1901, p. 586. 

C.I.P.W. : Journ. Geol., xiv, 1906, p. 692. 

L. Milch : Fort, der Min. Krist. u. Pet., ii, 1912, p. 163. 

U. Grubenmann : Fort, der Min. Krist. u. Pet., ii 1912. 
p. 208. 

Theralite, Rosenbusch, 1887. -- A phanerocrystalline 

rock composed essentially of labradorite, nepheline 

and purple augite, and often containing soda- 

amphiboles and biotite, or both. Analcite may 

be present, and most examples are olivine bearing. 

(Duppau, Bohemia.) 
G. W. Tyrrell : Geol. Mag., 1912, p. 79. 

A. Lacroix : C.R., clxx, 1920, p. 20; Geol. Mag., 1920, p. 

Thermal Metamorphism. A variety of meta- 

morphism in which recrystallisation is due to high 
temperature, the latter not being a consequence of 
dynamic processes, or of the introduction of mag- 
matic emanations. 
For References see under Metamorphism. 

Thin Sections. Flakes or slices of a rock or mineral 
which have been ground down until their thick- 
ness is reduced to nearly a thousandth of an inch, 
and mounted on object-glasses for microscopic in- 
vestigation. For most purposes the thickness of 
the finished section should be about 30 microns 
(30 ^=0.03 mm.). 

H. J. Grayson : Proc. Roy. Soc. Victoria, xxiii, 1910, p. 65. 
G. F. H. Smith : Min. Mag., xvi, 1913, p. 317. 
A. Holmes : Petrogra-phic Methods and Calculations, 1920. 

Tholeiite, Steininger, 1840. A term applied to 
porphyritic basalts characterised by the presence 
of phenocrysts of labradorite or bytownite in an in- 
ter sertal groundmass containing glass and occult 
free silica. (Tholei Schaumberg.) 

G. W. Tyrrell : Geol. Mag., 1917, p. 350. 

Thoulet Solution. A yellowish green transparent 
aqueous solution of potassium mercuric iodide, 
having a maximum specific gravity of 3.19. Also 
known as Sonstadt Solution. 


Tilaite, Duparc & Pearce, 1905. A melanocratic 
variety of olivine-gabbro or olivine-eucrite contain- 
ing pyroxenes and olivine with subordinate felspar 
(bytownite to anorthite) and small amounts of 
hornblende, biotite, apatite and magnetite. 

(Tilai Kamen, N. Urals.) 
L. Duparc P. Pamfil : Bull. Soc. Min. France, xxxiii, 

1910, p. 358. 

Tillite, Penck. A term applied to consolidated 
boulder-clays formed during glacial epochs 
anterior to that of the Pleistocene. 
A. P. Coleman : Bull. Geol. Soc. Am., xix, p. 347. 
Smithson. Ref. (1916), Pub. No. 2458, 1917, p. 264. 

Timazite, Breithaupt. A variety of greenstone con- 
taining white felspar, hornblende, and in some 
varieties quartz ; considered to be an altered deriva- 
tive from augite-dacite or augite-andesite. 

Tinguaite, Roscnbusch, 1887. A dyke rock, often 
porphyritic, having the composition of an aegirine- 
phonolite, and differing from solvsbergite by the 
presence of nepheline. 

(Serra de Tingua, Brazil.) 
W. C Brogger : Eru-ptivgest. Kristiania, i, 1894, p. 109. 

Tjosite, Brogger , 1898. -- A porphyritic syenite- 
lamprophyre containing augite, olivine, apatite, 
and magnetite in a matrix of anorthoclase laths. 
Cf. Kvellite. (Kirchspiel Tjose, Laurvik.) 

Toadstone. An old local name for the contemporane- 
ous amygdaloidal basalts of the Carboniferous 
Limestone of Derbyshire. The name either sug- 
gests a resemblance between the amygdales and 
the spots of a toad's skin, or is an anglicised 
variant of todtstein, in reference to the absence of 
lead ore. 
H. H. Arnold-Bemrose : Q.J.G.S., Ixiii, 1907, p. 241. 

Toellite, Pichler, 1873. A variety of porphyrite con- 
taining phenocrysts of biotite, hornblende, and 
garnet with some of andesine and quartz, in a 
microgranophyric groundmass ; = Tollite. 

(Toell, Tyrol.) 


Tonalite, v. Rath, 1864. A quartz-diorite containing 
hornblende and biotite as the chief mafic minerals. 

(Tonale, Tyrol.) 

Tdnsbergite, Brogger, 1890. -- A red laurvikite-like 
rock, in which the felspars are orthoclase and 
andesine. Some varieties are porphyritic. 

(Tonsberg, S. Norway.) 

Topazoseme, Haily, 1822. A rock composed essen- 
tially of topaz, quartz, and tourmaline. 
Topsailite, Lacroix, 1911. A lamprophyric rock (in- 
termediate in type between camptonite and 
kersantite), containing- phenocrysts of plagioclase 
(about An 50 ), augite, apatite, and titanoferrite, in 
a groundmass composed of andesine, biotite, 
barkevikite, augite and sphene. 

(C. Topsail, Los Is.) 

A. Lacroix : Nouv. Arch, du Mus. de Hist. Nat., 5 (iii), 
IQII, p. 78. 

Torbanite, Liversidge, 1881. An extreme variety of 
oil-shale, containing some 70 to 80 per cent, of 
carbonaceous matter, including an abundance of 
spores. It is a dark-brown substance, having a 
dull lustre, a yellow-fawn streak and a low specific 
gravity 1.2 to 1.3. 

Mem. Geol. Surv. Scot. (Oil Shales of the Lothians), and 
Ed., 1912, p. 159. 

H. R. J. Conacher : Trans. Geol. Soc. Glasgow, xvi, 1917, 
p. 164. 

Tordrillite, Spurr ) 1900. A hololeucocratic variety of 
rhyolite, characterised by the absence of mafic 
minerals, and corresponding chemically to alaskite. 

(Tordrillo Mts., Alaska.) 

Toscanite, Washington, 1897. A variety of quartz- 
trachyandesite ; i.e., a volcanic rock intermediate 
in its characters between rhyolite and dacite. 

(Tuscany, Italy.) 
H. S. Washington : Journ. Geol., v, 1897, p. 37. 

Tourmaline-corundum Rocks, Scrivenor, 1910. 

Very hard and fine-grained rocks of blue-black 
colour, having the mineral composition indicated 


by their name. Under the microscope they show 
oolitic structure, indicating that they are probably 
due to the intense metamorphism of oolitic cherts 
by granite. (Kinta, Malay States.) 

J. B. Scrivenor : Q.J.G.S., Ixvi, IQIO, p. 435. 

W. R. Jones : Q.J.G.S., Ixxii, 1916-17, p. 178. 

Tourmalinisation. A term applied to the processes, 
late-magmatic or pneumatolytic, whereby pre- 
existing minerals or rocks are replaced wholly or 
in part by tourmaline. 

J. S. Flett : Mem. Geol. Surv. 347 (Bodmin and St. Austell), 
1909, p. 65. 

C. E. Tilley : Trans. Roy. Soc., S. Australia^ xliii, 1919, 

P- i5 6 - 

Trachyandesite, Michel-Levy, 1894. A general term 
for rocks intermediate between trachyte and 
andesite, and generally containing phenocrysts of 
oligoclase or andesine in a trachytic groundmass, 
the felspar microlites of which are potash 

H. S. Washington : Journ. Geol., v, 1897, p. 367. 

Trachybasalt, Boricky, i^^. = Tephrite (in part),- 
monchiquite (in part). 

Trachydolerite, Abich, 1841. - - A general term for 
trachytic rocks containing labradorite in addition 
to orthoclase, or basaltic rocks containing ortho- 
clase in addition to labradorite; i.e., for rocks in- 
termediate in character between trachyte and 
H. S. Washington : Journ. Geol., v, 1897, p. 350. 

Trachyte, Brongniart, 1813. -- An aphanitic volcanic 
rock, generally porphyritic, containing alkali- 
felspars, and one or more mafic minerals, of which 
biotite and augite are those most usually 

G. W. Tyrrell : Proc. Roy. Soc. Edin., xxxvi, 1917, p. 288. 
Mem. Geol. Surv. Scot. (East Lothian), 1910, p. 127. 

Trachytic Texture. A texture in which neighbour- 
ing felspar laths of a microlitic groundmass have 
a sub-parallel disposition, corresponding to the 


stream lines of the nearly consolidated lava or 

Trachytoid Phonolite. A general term for varieties 
of nepheline-phonolite, containing preponderant 
alkali-felspars, and consequently having a trachytic 
texture ; contrasted with nephelinitoid phonolite 
in which nepheline is the preponderant felsic 

Trachytoid Texture. A texture in which the pris- 
matic felspars of a phanerocrystalline rock have a 
parallel or sub-parallel disposition, as for example 
in many varieties of alkali- and nepheline-syenites. 

Traction, Gilbert, 1914. A general term for that 
mode of transport of debris by running water, in 
which the particles are swept along close to the 
bed of the stream by rolling, sliding, or saltation ; 
contrasted with suspension. 
G. K. Gilbert : U.S.G.S. Prof. Pa-p., 86, 1914, p. 15. 

Trap. An old Swedish name originally applied to 
igneous rocks which were neither coarsely crystal- 
line, like granite, nor cellular and obviously vol- 
canic, like pumice and scoria. The rocks so 
designated included basaltsi, dolerites, andesites, 
and porphyrites (types often grouped as whin- 
stones) ; altered varieties of some of these, such 
as epidiorite and diabase (types grouped as green- 
stones) ; and, finally, the mica-traps or lampro- 

Trap-shotten Gneiss, King & Foot, 1864. A term 

applied to gneiss impregnated with nearly black in- 
durated material originally supposed to be in- 
jections of "trap" rock, but now identified with 
" flinty crush-rock." Cf. Pseudo-tachylyte. 
T. H. Holland : Mem. Geol. Surv. India, xxviii, 1900, pp. 
198, 248. 

Trass. A local Italian name applied to pumiceous 
tuffs which are utilised for the manufacture of 
hydraulic cement. 

Travertine. A variety of calcareous tufa, of light 
colour, often concretionary and compact, but vary- 


ing- considerably in structure, some varieties being 
extremely porous. Cf. Onyx Marble. 
W. H. Weed : U.S.G.S. gth Ann. Ref., 1887-8, 1890, p. 619. 

Trichite, Zirkel, 1873. A thin filament or hair-like 
form of crystallite, often occurring- in irregular or 
radiating groups. 
" F. Rutley : Min. Mag., ix, 1891, p. 263. 

Tripoli, WaUeriuS t 1747. -- A fine powdery siliceous 
deposit composed of the tests of diatoms and 

Troctolite, v. Lasaulx, 1875. A phanerocrystalline 
rock composed essentially of labradorite or bytown- 
ite and olivine (always more or less serpentinised), 
with little or no augite. Cf. Ossypite. 
T. G. Bonney : Geol. Mag., 1885, p. 439. 
J. S. Flett : Mem. Geol. Surv. 359 (Lizard), 1912, p. 85. 

Trowlesworthite, Worth, 1884. A pneumatolytic 
modification $>f granite containing orthoclase, tour- 
maline and fluorspar with residuary quartz. 

(Trowlesworthy, Cornwall.) 

Tsingtauite, Koto, 1909. A variety of granite- 
porphyry having- phenocrysts of orthoclase in a 
fine-grained granitic groundmass. 

(Tsingtau, Korea.) 
B. Koto : Journ. Col. Sci. Tokyo, xxvi, 1909, p. 186. 

Tufa. A porous, concretionary or compact formation 
of calcium carbonate deposited around springs. 

Tuff. A rock formed of compacted pyroclastic frag- 
ments, some of which can g-enerally be distin- 
guished as such by the naked eye. If the larger 
fragments exceed the size of walnuts the rock be- 
comes an agglomerate, or a volcanic breccia. 
According as the prevalent constituents are frag- 
ments of crystals, rocks or glass, crystal, lithic and 
vitric types of tuffs are recognised. Cf. Ash. 
L. V. Pirsson : Am. Journ. Set., xl, 1915, p. 191. 
J. F. N. Green : Proc. Geol. Assoc., xxx, 1919, p. 165. 

Tuffite, Miigge, 1893. A general term for composite 
clastic rocks, in which both volcanic (pyroclastic) 


and detrital (epiclastic) materials are present in 
considerable amount. 

TllSCUlite, Cordier, 1868. A variety of melilite- 
leucitite containing- only small amounts of pyrox- 
ene, ilmenite, and felspar. 

(Tusculum, Italy.) 

Typomorphic, Becke. -- A term applied to minerals 
characteristic of the particular set of physical con- 
ditions which controlled their formation. 


Uintaite. A black lustrous variety of bitumen having 
a conchoidal fracture, and thus resembling manjak. 
It differs from albertite by being- completely soluble 
in turpentine, and, partly so, to the extent of 45 
per cent., in alcohol ; Gilsonite. 

(Uintah Co., Utah.) 

G. H. Eldridge : U.S.G.S. 22nd Ann. Re-p., Pt. i, 1901, pp. 
221, 340. 

Ulrichite, Marshall, 1906. A somewhat melanocratic 
variety of tinguaite containing large phenocrysts 
of alkali-felspars, nepheline, and soda-pyroxenes 
and amphiboles, with smaller phenocrysts of olivine 
and analcite. 

P. Marshall : Q.J.G.S., Ixii, 1906, p. 397. 
A. Holmes : Geol. Mag., 1915, p. 366. 

Ultrabasic Rocks, Judd, 1881. -- A general term ap- 
plied to igneous rocks containing little or no fel- 
spar, but characterised essentially by one or more 
of the common mafic minerals, such as olivine, 
pyroxenes, amphiboles, etc. Chemically, ultra- 
basic rocks have been described as those having a 
percentage of silica less than that of anorthite, the 
limiting fig-ure being about 45 per cent. 

Ultrametamorphism, Holmquist, 1909. A general 
name for processes of so extreme a character that 


the rocks affected pass wholly into a magmatic 
condition. Cf. assimilation^ anatexis, palin- 
genesis, syntexis. 

Ultra-mylonite, Quensel, 1916. A variety of mylonite 
in which primary structures and porphyroclasts 
have been entirely obliterated, so that the rock be- 
comes homogeneous and aphanitic with little sign, 
if any, of parallel structure ; = Flinty crush-rock. 
Cf. Hartschiefer. 
P. Quensel : Bull. GeoL Inst, U$sala, xv, 1916, p. 103. 

Umptekite, Ramsay, 1894. A variety of alkali-syenite 
composed essentially of alkali-felspars and soda- 
amphiboles. (Umptek, Kola Peninsula.) 

P. Quensel : Bull. Geol. Inst. U-psala, xii, 1914, p. 142. 

Unakite, Bradley, 1874. A variety of granite contain- 
ing quartz, pink felspar and green epidote. 

(Unaka Range, N. Carolina.) 
T. L. Watson : Am. Journ. Sci., xxii, 1906, p. 248. 

Uncompahgrite, Larsen. A term applied to an ex- 
tremely coarse-grained rock, containing 70 per 
cent, or more of melilite, with small amounts of 
pyroxene, magnetite, perovskite, and apatite. 
(Uncompahgre, Colorada.) 

E. S. Larsen & J. F. Hunter : Journ. Wash. Acad. Sci., iv. 
iQH, P- 473- 

Undersaturated, Shand, 1913. - - A term applied to 
rocks wholly or partly composed of unsaturated 
minerals; e.g., felspathoids and olivine. 

S. J. Shand: Geol. Mag., 1913, p. 313; 1915, P- 34- 

A. Holmes : Geol. Mag., 1917, p. 124. 

Unequal Pressure. See Directed Pressure. 

Ungaite, ladings, 1913. A general name suggested 
for oligoclase-dacites. (Unga Is., Kamchatka.) 

Unsaturated, Shand, 1913. A term applied to mine- 
rals (e.g., felspathoids and olivine) which do not 
normally occur in association with free silica ; also 
applied to rocks which contain only unsaturated 
minerals. (For references see Undersaturated.) 


Uralitisation. - - The processes whereby the primary 
pyroxene of igneous rocks is altered to uralite, a 
form of secondary hornblende paramorphic after 
augite, and generally, but not necessarily fibrous. 

G. H. Williams : U.S.G.S., Bull. 62, 1890, p. 52. 

L. Duparc & T. Hornung : C.R., cxxxix, 1904, p. 223. 

Urbainite, Warrzn, 1912. A facies of ilmenitite con- 
taining from 10 to 20 per cent, of rutile, and from 
3 to 5 per cent, of sapphirine. 

(St. Urbain, Quebec.) 

C. H. Warren : Am. Journ. Sci., xxxiii, 1912, p. 275. 

Ureilite, Jerofejeff & Latschinoff, 1888. A coarse- 
grained achondritic meteorite composed of olivine 
and augite enclosed in a fine mesh of nickel-iron 
with carbonaceous matter (including diamond). 
The type is practically equivalent to a pallasite with 
less than 10 per cent, of nickel-iron. 

Urtite, Ramsay, 1896. - - A phanerocrystalline rock 
composed of nepheline (85 per cent.), aegirine (12 
per cent.), and accessory apatite. 

(Lujaur Urt, Kola, Finland.) 

W. Ramsay : G eol. For en i Stockholm Forhandl., xviii, 1896, 
p. 463 ; Fennia, xv, 2, p. 22. 

Vadose, Posepny, 1894. A term applied to seepage 
waters occurring below the surface and above the 
water-table ; contrasted with phreatic, which refers 
to the ground-water below the water-table. 
R. A. Daly : Econ. Geol., xii, 1917, p. 494. 

Valbellite, von Schaever, 1898. A fine-grained variety 
of peridotite composed of olivine, hypersthene, and 
hornblende ; pyrrhotite is locally an abundant con- 
stituent ; = Hornblende-harzburgite. 

(Val Bella, Piedmont.) 

Vallevarite, Gavelin, 1915. A somewhat leucocratic 
monzonitic rock composed largely of andesine- 


microcline-antiperthite, with small amounts of 
diopside, biotite, titanoferrite and apatite. 

(Vallevara, Sweden.) 

A. Gavelin : Geol. For. i Stockholm Fork., xxxvii, 1915, 

p. 19. 

Van der Kolk Method. A microscopic method for 
determining whether the refractive index of a 
mineral grain is higher or lower than that of a 
liquid medium in which it is immersed and viewed. 
Light rays from below the stage are cut off by in- 
serting a suitable obstacle, and as the grain acts as 
a lens, and the eyepiece inverts, the image, a 
shadow appears (a) on the same side as the 
when the grain has the higher refractive index, 
(b) on the opposite side when the grain has the 
lower index. 

J. L. C. Schroeder van der Kolk : Tabellen zur mikrosco- 
pischen Bestimmung der Mineralien nach ihrem Brech- 
nungsindex. Wiesbaden, 1906. 

Variation Diagram. -- A graphical representation of 
the variation in composition of the members of a 
series of related igneous rocks; e.g. , by plotting 
the bases as ordinates against silica as abscissae. 

A. Marker : Nat. Hist. Ig. Rocks, 1909, p. 119. 

H. H. Robinson : U.S.G.S. Prof. Pa-p., 76, 1913, figs. 32-5. 

H. C. Richards : Proc. Roy. Soc. Queensland, 1916, p. 200. 

A. Holmes : Q.J.G.S., Ixxii, 1916-17, p. 264. 

Variolite, Aldrovande, 1648. -- An aphanitic basaltic 
or andesitic rock containing numerous felspathic 
spherulites with radial texture (varioles). 

G. A. J. Cole & J. W. Gregory : Q.J.G.S., xlvi, 1890, p. 295. 

G. W. Tyrrell : Trans. Geol. Soc. Glasgow, xiv, 1912, p. 291. 

Variolitic Structure. A structure akin to spherulitic 
structure occurring in basaltic rocks and especially 
in the tachylytic margins of small intrusions and in 
certain varieties of pillow-lavas known as variolites. 
In some cases the spherulites are made up of 
minute radiating fibres of plagioclase with inter- 
stitial glass, and in others they are less regular and 
consist of interferent sheaf-like groups of labra- 


dorite rods diverted by grains of augite, olivine, or 

A. Harker : Nat. Hist. Ig. Rocks, 1909, p. 275. 

Varnsingite, Sobral, 1913. -- A coarse-grained dyke- 
rock essentially composed of albite and augite, 
with accessory sphene, apatite, and magnetite ; 
regarded as a pegmatoid derivative from a gabbro 
magma. (Nordringa District, Sweden.) 

Vaugnerite, Fournet, 1836. A variety of quartziferous 
monzonite characterised by an unusual abundance 
of biotite and apatite. (Vaugneray, France.) 

A. Lacroix : Bull. Soc. franf. Min., xl, 1917, p. 158. 

Vein. An irregular sinuous, igneous injection, or a 
tabular body of rock formed by deposition from 
solutions rich in water or other volatile substances. 

Vein-quartz. A rock of pegmatitic or hydrothermal 
origin consisting essentially of interlocking sutured 
crystals of quartz, the individuals varying widely in 

Venanzite, Sabatini, 1898. A holocrystalline porphy- 
ritic rock occurring as a lava flow, composed of 
phenocrysts of olivine and phlogopite in an apha- 
nitic groundmasis of these minerals, together with 
melilite, leucite and magnetite. Rosenbusch gave 
the name Euktolite to this rock, not knowing that 
it had already been described. 

(San Venanzo, Umbria.) 

Verite, Osann, 1889. A black lamprophyric pitchstone 
containing crystals of phlogopite or biotite, augite, 
and olivine, with little or no modal felspar; the 
chemical composition is similar to that of the 
melanocratic trachytes and minettes. 

(Vera, Cabo de Gata, Spain.) 

Vermicular Quartz. A term applied to quartz occur- 
ring in worm-like forms intergrown with or pene- 
trating felspars ; = quartz de corrosion. 
}. J. Sederholm : Bull. Comm. Geol. Finlande, No. 48, 1916, 
p. 63. 



VeSUVite, Lacroix, 1917. A variety of leucite-tephrite 
rich in leucite. (Vesuvius.) 

A. Lacroix : C.R., clxv, 1917, p. 482. 

Vicoite, Iddings, 1915. A variety of leucite-tephrite 

characterised by the presence of orthoclase ; = leu- 

cite-shoshonite. (Vico Volcano, Italy.) 

J. P. Iddings & E. W. Morley : Journ. GeoL, xxiii, 1915, 

P- 2 34- 

Vintlite, Pichler, 1875. A porphyritic variety of horn- 
blende-dolerite containing phenocrysts of labra- 
dorite or bytownite and brown hornblende in a 
fine-grained groundmass of felspar and horn- 
blende, with a little quartz. 

(Vintl, near Klausen, Tyrol.) 

Viridite, Vogelsang, 1872. -- A general term for ob- 
scure green alteration products (including chloritic 
minerals, serpentine, etc.), which cannot be, or 
have not been specifically diagnosed. 

Viscosity. - - Any resistance to deformation that 
involves dissipation of energy by internal friction. 
Viscosity of Fluids. The property of imperfect fluids 
whereby they resist the action of a shearing stress ; 
measured by the shearing stress required to cause 
flow at a certain constant rate. 
F. F. Grout : Journ. Geol., xxvi, 1918, p. 485. 
A. L. Field & P. H. Royster : Trans. Am. Inst. Min. Eng., 
Iviii, 1918, p. 658. 

Viterbite, Washington, 1906. -- A variety of leucite- 

trachyte containing abundant large phenocrysts of 

leucite. (Viterbo, Italy.) 

H. S. Washington : Carnegie Inst. Wash., Pub. No. 57 

(Roman Comagmatic Region], 1906, p. 35. 

Vitrain, Slopes, 1919. A term suggested for the 
vitreous variety of " bright " coal. In bituminous 
coals it occurs as narrow, compact brilliant bands 
which break into small cube-like pieces or into irre- 
gular fragments with conchoidal fracture. The 
fine banding characteristic of clarain is not 
developed in vitrain, which, under the microscope, 


is seen to be uniform and structureless, the colour 
in thin sections being- from yellow to amber. 
M. C. Stopes : Proc. Roy. Soc. B., xc, 1919, p. 475. 
Vitric Tuffs, Pirsson, 1915. Volcanic tuffs or ashes 
mainly composed of comminuted fragments of 
glass. Cf. lithic and crystal tuffs. 
L. V. Pirsson : Am. Journ. Sci., xl, 1915, p. 191. 

Vitro-. A prefix added to the names of rocks to in- 
dicate the presence of abundant glass, e.g., Vitro- 
basalt ; = hyalobasalt. 

Vitrophyre, Vogelsang, 1867. -- A general term for 
porphyritic rocks having the composition of quartz- 
porphyry or orthophyre, but differing- from these 
by the possession of a glassy groundmass. 

Vogesite, Rosenbusch, 1887. A syenitic lamprophyre 
of which the mafic minerals are generally horn- 
blende, and sometimes augite, the dominant fel- 
spar being oligoclase or andesine when sufficiently 
fresh to be determined. (Vosges.) 

W. Cross : U.S.G.S., Prof. Pa-p., goC, 1914, p. 21. 

Volatile Fluxes, Evans, 1910. A general term for the 
volatile constituents of magmas. 

T. C. Chamberlain : Carnegie Inst. Washington, Pub. No. 
106, 1908. 

A. L. Day & E. S. Shephard : Bull. Geol. Soc. Am., xxiv, 

!9*3> P- 573- 

Volcanic Dome. A volcanic form consisting of 
rounded masses of viscous lava squeezed out from 
the orifice, or of portions of older lavas or ejecta- 
menta elevated by the pressure of new lava rising 
from beneath. The term dome is also applied as 
a geographical term to volcanic mountains of the 
type of Mauna Loa. 

A. Lacroix : La montagne Pelee et ses eruptions, 1906, p. 
no; La montagne Pelee a-pres ses eruptions, 1908, p. 31, 

S. Powers : Am. Journ. Sci., xlii, 1916, p. 261. 

Volcanic Mud and Sand. Deposits occurring around 
volcanic oceanic islands and coast-lines. The 
deposits near shore contain fragments of volcanic 
rocks and minerals, and are referred to as sands, 


while further out the finer particles and alteration 
products form clayey or chloritic muds. 
J. Murray & A. F. Renard : " Challenger " Rep. (Deep Sea 

Deposits), 1891, p. 240. 

Vokanite, Hobbs, 1893. A volcanic rock composed 
essentially of anorthoclase and augite, and having 
the chemical composition of dellenite. 

(Volcano, Lipari Is.) 

W. H. Hobbs : Bull. Geol. Soc. Am., v, 1893, p. 598. 
A. Lacroix : C.R., cxlvii, 1908, p. 1491. 

Volhynite, Ossovski, 1885. A variety of quartz- 
kersantite containing- phenocrysts of plagioclase 
and hornblende, with or without biotite, in a 
groundmass of quartz and felspar with abundant 
chlorite. (Volhynia, Russia.) 

Vug or Vugh. A mining term for an unfilled cavity 
in a vein, generally with a mineral lining of dif- 
ferent composition from that of the immediately 
surrounding ore. 

Vulsinite, Washington, 1896. A variety of trachy- 
andesite, similar to banakite, but somewhat richer 
in potash. 

(Bolsena, Vulsinian district, Italy.) 
H. S. Washington : Journ. Geol., iv, 1896, p. 55. 


Wacke. An old term for a dark green to brownish 
black earth or clay formed as the final residual 
decomposition product of basaltic rocks and tuffs. 
Weathering. The destructive alteration and decay of 
rocks by exogenetic processes acting at the surface 
and down to the depth to which atmospheric oxy- 
gen can penetrate. 

G. P. Merrill : Rocks, Rock Weathering and Soils, 1906. 

E. Steidtmann : Econ. Geol., iii, 1908, p. 381. 

J. W. Evans: Proc. Geol. Assoc., xxiv, 1913, p. 245; xxv, 
1914, p. 229. 

E. Weinschenk (Trans, by A. Johannsen) : Fundamental 
Principles of Petrology, 1916, p. 73. 


Websterite, Williams, 1890. A variety of pyroxenite 
composed of both monoclinic and orthorhombic 

Wehrlite, Kobell, 1839. A variety of peridotite con- 
taining diallage. The name is now extended to 
include with diallage all other varieties of mono- 
clinic pyroxenes. 
M. E. Schuster : Geognost, Jahresheft, xviii, 1907, p. 43. 

Weiselbergite. A variety of micro-porphyritic 
dolerite having a microlitic texture resembling that 
of augite-andesite. Crystals of labradorite, 
augite, and iron-ores are embedded in a ground- 
mass composed of plagioelase and augite microlites 
with interstitial glass. 

(Weiselberg, Nahe District.) 

Welded Dykes, Weinschenk. A term applied to peg- 
matitic and aplitic dykes, the boundaries of which 
have been obliterated by continued growth of the 
minerals of the granite into which the dykes have 
been injected. 

Wennebergite, Schuster, 1905. A variety of quartz- 
iferous porphyry characterised by phenocrysts of 
orthoclase, biotite, and quartz, in a microcrys- 
talline and chloritic groundmass containing abun- 
dant apatite and sphene. (Wenneberg, Ries.) 

Whinstone. A popular general name for dark col- 
oured rocks such as dolerite, basalt, porphyrite, 
andesite, etc., which are comparatively unaltered, 
intrusive or interbedded, have a crystalline texture 
not usually coarse, and are composed of the 
minerals felspar, pyroxene, and iron-ores, with or 
without hornblende or olivine. As a trade-name, 
it is recommended by the British Engineering 
Standards Association that the term whinstone 
should be strictly confined to rocks which come 
under the trade heading of basalt. According to 
the same authority the latter includes basalt, 
diabase, dolerite, epidiorite, greenstone, lampro- 


phyre, spilite, and teschenite. According to this 
usage whinstone is made to cover both whinstones 
and greenstones, and includes types which collec- 
tively have usually been known as trap-rocks. Cf. 

A. Holmes : Geological and Physical Characters of Concrete 
Aggregates, B.F.P.C. " Red Book," 256, 1920, p. 40. 

Wichtisite. A modification of dolerite rich in glass 
occurring as selvages in sills or dykes or as small 
independent intrusions. 

(Wichtis, near Helsingfors, Finland.) 

Wilsonite. A rhyo-andesite tuff containing fragments 
of pumice and andesite in a matrix consisting of 
shreds of glass in a granular isotropic base. The 
rock has also been interpreted as a brecciated 
rhyolite flow, but the evidence appears to be against 
this view. (Owharoa, Hauraki, N.Z.) 

Geol. Surv. N . Zealand, Bull. 16, 1913, p. 70. 

Windsorite, Daly, 1903. A leucocratic variety of 
quartz-monzonite, containing a small percentage of 
biotite. (Windsor, Vermont. 

R. A. Daly : U.S.G.S. Bull., 209, 1903, p. 45. 

Woodendite, Skeats & Summers, 1912. A variety of 
orthoclase-bearing basalt resembling absarokite. 

(Woodend, Victoria.) 

E. W. Skeats & S. Summers : Geol. Surv. Victoria, Bull. 
24, 1912, p. 31. 

Wurtzilite. A massive, black, elastic bituminous sub- 
stance, having a brilliant lustre and a conchoidal 
fracture. It differs from members of the asphaltite 
group not only in its elasticity, but also in resist- 
ing the usual solvents. 

Wyomingite, Cross, 1897. A porphyritic dyke-rock 

with phenocrysts of phlogopite in an aphanitic 

groundmass containing leucite and diopside ; 

= phlogopite-leucite. (Wyoming.) 

W. Cross: Am. Journ. Set., iv, 1897, p. 120. 



Xenoblast, Becke, 1903. A term applied to crystals 
which have grown during metamorphism without 
the development of their characteristic faces. Cf. 

Xenocryst, Sollas, 1894. A term applied to allo- 
thigenous crystals, generally corroded, that are 
foreign to the igneous rock in which they occur. 

Xenolith, Sollas, 1894. A term applied to allothi- 
genous rock fragments that are foreign tO' the ig- 
neous rock in which they occur ; = accidental in- 
clusion, = exogenous enclosure, enclave enallo- 

A. Harker : Mem. Geol. Surv. (Tert. Ig. Rocks Skye), 1904, 
P- 35 1 - 

Yamaskite, Young, 1906. A medium or fine-grained 
rock composed of basaltic hornblende and titan- 
augite, with a small amount of anorthite, and 
accessory iron-ores and biotite ; olivine-bearing 
varieties are also known. 

(Mt. Yarnaska, Quebec.) 

J. J. O'Neill : Geol. Surv. Canada, Mem., 43 (Pub. No. 
1311), 1914, p. 64. 

Yatalite, Benson, 1908. A pegmatoid rock (associated 
with a titaniferous series of diopside-syenites 
and diorites) containing as its chief constituent 
uralitic actinolite (after diopside) with poikilitic 
inclusions of magnetite and sphene. The other 
minerals present are albi.te with microcline titani- 
ferous magnetite, apatite and sphene. 
W. N. Benson : Trans, and Proc. Roy. Soc. S. Australia, 
xxxiii, 1909, p. 126. 

Yentnite, Spurr, 1900. A coarse-grained granitoid 
rock essentially containing primary scapolite, 


plagioclase (oligoclase-andesine), and biotite ; 
= scapolite-belugite. (Yentna R., Alaska.) 

J. E. Spurr : Am. Journ. Sci., x, igoo, pp. 310-15. 

Yogoite, Weed, & Pirsson, 1895. A melanocratic 
facies of syenite containing augite and orthoclase, 
with smaller amounts of biotite and oligoclase-an- 
desine. (Yogo Peak, Montana.) 

W. H. Weed & L. V. Pirsson : Am. Journ. Sci., 1, 1895, 
p. 472; li, 1896, p. 351. 

Zeolitisation, Lacroix, 1896. - - The process whereby 
the felspars and other alumino-silicates of a rock 
are transformed into zeolites. 
A. Lacroix : Min. de la France, ii, 1896, p. 45. 

Zobtenite, Roth, 1887. A variety of gabbro-gneiss 
containing knots or eyes of diallage surrounded by 
streams of uralite and embedded in a granular 
mass of epidote and plagioclase (saussurite). 

(Zobtenburg, Silesia.) 

Zoning. A term applied to the structure of a mix- 
crystal which is composed of isomorphous com- 
pounds arranged in layers or zones of different com- 
position ; successive zones having been deposited 
from a magma (or other liquid solution), which 
gradually changed in composition owing to the 
separation of crystal phases. 

N. L. Bowen : Am. Journ. Set., xl, 1915, p. 180, and Journ. 
Geol. Su-p-p., vol. xxiii, 1915, p. 38. 

2 4 3 



Adelogene, aphanitic. 

Affleurement, outcrop ; exposure. 

Agents mineralisateurs, mineral- 
ising agents. 

Agregees (Roches} , clastic 
(rocks) . 

Aiguille, needle (acicular min- 
eral) ; spine (e.g. of Mount 

Alluvion, alluvium. 

Alluvion aurifere, placer. 

Amas, stockwork. 

Amiante, asbestos. 

Amphigene, leucite. 

Amphlgenite (Cordier, 1868), 
leucite-tephrite and other 
basaltic rocks containing 

Anagenite, conglomerate formed 
of fragments of granite, gneiss 
or schist. 

Ancienne (eruptive), term ap- 
plied to pre-Tertiary igneous 

Anorthose, plagioclase (Celesse); 
now used for anorthoclase. 

Arendalite, garnet rock. 

Ardoise, slate. 

Argile, clay. 

Argile smectique, Fuller's earth. 

Argileuse, argillaceous. 


Btonnee (structure) , mortar 

Boue, mud; ooze. 

Boules (division en), spheroidal 
partings in igneous rocks. 

Bulle, gas bubble, in inclusions 
of minerals. 

Bulleuse, vesicular. 

CaiilOUtis, gravel. 

Calcaire, limestone. 

Cargneule, cellular dolomite. 

Cassure, fracture. 

Chaille, siliceous concretion. 

Chalumeau, blowpipe. 

Charriage, overfold. 

Cheires, flows of block-lava ; = 

Chevauchement, overfold, thrust. 

Cicatrisation, healing of broken 
or corroded crystals by a 
secondary deposit of the same 
material in optical continuity. 

Colonnes filtrantes, streams of 
hot gases rising from the 
earth's interior. 

Compose, heterogeneous, compo- 

Corindon, corundum. 

Corne'enne, hornfels. 

Cornes, hornfels, adinole and 
allied products of contact 

Corrosion, quartz de, see quartz 

Couche, bed or stratum. 

Coulee, lava stream or flow. 

Couronne, corona. 

Craie, chalk. 

CulOt, plug (volcanic). 

2 44 



D6lit, joint. 

Diaclase, joint. 

Dipyrisation, scapolitisation. 

Disthene, kyanite. 

Domaine, province (petrographi- 

Durete, hardness. 

Eclat, lustre. 

Ecoulement (structure d'), flow 
or fluxion structure. 

Eluviale, residual (deposits). 

Enclaves enallogenes (Lacroix), 
xenoliths or accidental inclu- 
sions. (See page 90.) 

Enclaves homceogenes (Lacroix), 
autoliths or cognate inclusions. 

Epanchement (Roches <2'), effu- 
sive or volcanic rocks. 

Epontes, walls of the country 
rock enclosing a dyke or vein. 

Exomorphisme, contact mctamor- 
phism of the rocks invaded by 
a magma. 

En coin, cuneMforme, wedge- 

Entrecroisee (stratification], 
cross-- or current-bedded. 

Endomorphisme, modifications 
produced in a magma (and 
hence in the resulting rock) 
by interaction with the rocks 

Entroques (calcaire a) , crinoidal 

Epontes, walls of veins or dykes. 

Faille, fault. 

Faluns, shelly beds (Tertiary); 


Farine fossile, diatom earth. 
Fenestre~e (structure"], lattice 

structure (e.g. of serpentine 

after hornblende) . 
Feuilletee, foliated. 
Filon, vein, dyke. 

Filon couche. sill. 
Fluorine, fluor spar. 
Forage, boring. 


Galet, pebble, shingle. 

Gemme, gem ; Sel genime = rock 

Gisement, deposit; formation. 

Gite metallifere, metalliferous 

Glanduleuse (structure], augen 
or phacoidal structure. 

Globulaire, spherulitic. 

Grand, coarse sand; fine gravel. 

Granitelle, a leucocratic quartz- 
felspar granite. 

Granitite, a two mica granite, or 
according to some authors a 
plagioclase granite (adamel- 

Granulite, muscovite-granite (cf. 
English usage of term) . 

Gravier, gravel. 

Grenat, garnet. 

Grenue (structure], granular, 
granitic, saccharoidal ; a term 
applied to holocrystalline rocks 
in which there is no apparent 
discontinuity in crystallisation. 

Gres, sandstone. 

Gries, detritus; intermediate in 
grade between graviers and 


Hemithrene, epidiorite rich in 


H6mitrope, twinned. 
Heteromorphique, heteromor- 

phic. (See page 117.) 
Houille, coal. 

Houille grasse, bituminous coal. 
Houille maigre, steam coal. 
Houille seche, cannel coal. 
Hyalomfcte, greisen. 

Inclinaison, dip. 


2 45 

Inclusions, term restricted to in- 
clusions (gas, liquid, glass or 
mineral) in minerals; not, as 
in English, also denoting 
xenoliths, etc. (cf. enclaves]. 

Kersanton, kersantite. 

Labrador, labradorite. 

Labradorite, olivine-free basalt. 

Laderes, sarsens (blocks of Eo- 
cene sandstone which have re- 
sisted denudation up to the pre- 
sent day). 

Leptoclase, a minute fissure. 

Lentille, lens. 

Libelles, gas inclusions in mine- 

Limon, loam. 

Lit, thin layer, lamina. 

Lithoclase, rock fracture (of any 


Made, twin. 

Maclifere, see Schiste macli- 

Macline, spotted slate, chiastolite 
slate, etc. 

Maillee (structure), mesh struc- 

Marne, marl. 

Menilite, nodules of opal. 

Microgrenue (structure}. The 
texture of a holocrystalline 
rock with apparent discontinu- 
ity in crystallisation (indicated 
by the presence of pheno- 
crysts) , the groundmass being 

Microlitiique (structure}. The 
texture of a porphyritic rock, 
the groundmass of which is 
composed largely of more or 
less idiomorphic tabular or 
prismatic crystals (e.g., felspar 
laths) with or without inter 
stitial glass. 

Minerai, ore. 

Minette, local name for the iron- 
ores of Lorraine. 

Miroirs de faille, slickensides. 

Mortier (structure en~) , mortar 

Moule, matrix. 


Nappe, sheet or flow (e.g., lava 

flow or sill) . 
Nu6e ardente, luminous cloud of 

ash and gases (formed during 

intense volcanic explosions of 

the Pelean-type). 

CEilUJ (gneiss}, augen gneiss. 

Oligiste, haematite. 

Ollaire (pierre), steatite; talc 


OphioHte, a term for serpentine. 
Orthose, orthoclase. 

Paieovolcanique, term applied 
to pre-Tertiary volcanic rocks. 

Paraclase, fault. 

Pate, magma. 

Pdte vitreuse, glassy base. 

Pendage or inclinaison, dip. 

Petrosiloceuse, felsitic. 

Phangrogene, coarsely granular 
or phanerocrystalline. 

Pli, fold. 

Plissement, fold. 

Phyllade, phyllite. 

PoidS sp6cifique, specific gravity. 

Ponce, pumice. 

POUdingue, puddingstone. 

Promorphisme, devitrification. 


Quartz de Corrosion -.- 

Quartz vermicule, drop-like in- 
clusions of quartz in felspar; 
intergrowths of quartz with 
plagioclase, as in myrmekite. 

2 4 6 


Recif corallien, coral reef 

R6tiulee (structure], netted 
structure (e.g., of serpentine). 

Rgtinite, pitchstone. 

Ride, ripple. 

Roches d'imbibition, rocks in- 
jected by granitic magma e.g., 
injection gneiss. 

Rubang, banded. 

Sable, sand. 

Salse, mud volcano. 

Schiste, slate. 

Schiste argileux, shale. 

Schiste cristalin, schist. 

Schiste maclifere, chiastolite 

" slate." 

Sel gemme, rock salt. 
Silex, flint. 

Stade, stage or period (e.g., of 

Synclase, contraction joints. 

Tachete' (schiste) , spotted slate or 

Terrains, formations, series of 

Tourbe, peat. 
Treillisee (structure] , lattice 

structure (e.g., of serpentine, 

after hornblende). 
Typhon, boss; stock; batholith. 

Vacuole, vesicle. 
Vermicu!6 (quartz), drop-like in- 
clusions of quartz in felspars. 
Vitreux, glassy. 

2 4 7 



Compiled by Miss J. H. ROBERTSON 

Abblatterung, exfoliation. 

Abgespalten, differentiated. 

Ablagerung, deposit. 

Abkiihlungsdifferentiation, liqua- 
tion in a magma before crystal- 

Abraum, detritus. 

Abraumsalze, sulphates and 
chlorides of potassium and ' 
magnesium (as in the Stassfurt 
deposits) . 

Absonderung, joint; parting (be-! 
tween two beds of rock) ; j 
cleavage or striation (e.g., of ; 
diallage) ; separation or segre- 
gation from a magma. 

Abteilung, formation or series 
(stratigraphical) . 

Abyssische Spaltung, abyssal 

Abzweigungen, apophyses. 

Aohatmandel, agate amygdules. 

Achsen, see Axen. 

Adergneis, injected or vein- 

Adern, veins. 

Adlagnostisch, indistinguishable, j 

Aftcrkrystall, pseudomorph. 

Agjregatzustand, solid state. 

Akzesscrlsch, accessory. 

Alteruptivgesteine, a general 
designation for pre-tertiary 
igneous rocks. 

Angeschmolzen, fused, welded. 

Asche, ash. 

Atmospharilien, atmospheric 
agents of weathering. 

Aufgenommene Gemengteile, as- 
similated constituents. 

Auflosung, solution. 

Auflosungsgrenze, limit of 
(microscopic) resolution. 

Ausbleichung, bleaching. 

Ausbruch, eruption. 

Ausfallung, precipitation. 

Ausfiillungsraume, infillings of a 

Aushauchung, exhalation. 

Auskeilen, to thin out. 

Ausjaugung, ilixiviation, leach- 

Auslaugungshohle, cavities or 
hollows due to solution or 

Ausloschung, extinction (between 
crossed nicols). 

AusloschungSSChiefe, extinction- 

Ausscheiden, to separate out. 

Austausch, exchange (e.g., of 
material in alteration pro- 
cesses) . 

Auswelchungsclivage, strain-slip 

Auswurflinge, la-pilli, ejectamen- 

Axenblld, interference-figure or 

Eanderung, a streak, stripe or 


Begleitende Bestandmassen, as- 
sociated constituents such as 
concretions and secretions. 

Begleitmineralien, associated 

load metamorphism. 

Beschaffenheit, constitution. 

Bestandteile, constituents. 

Beton, concrete. 

Beweglichkeit, mobility. 

BildlOS, amorphous, structure- 

Bildung, formation (of a rock). 

Bildungsweise, mode of forma- 

Bindemittel, cement. 

Biolithe, sediments of organic 

Blaschen, gas bubble (in inclu- 
sions) . 

Blasenraume, vesicles. 

Blatterstein, pillow-lava, vario- 
lite, or spilite. 

Blitzrohren, fulgurite. 

Blauschlamm, blue mud. 

Blocklehm, boulder-clay. 

Block-Strand, boulder-beach. 

Blutsverwandtschaft, consan- 

Bodenanalyse, soil analysis. 

Bogenstruktur, see p. 48. 

Bohnerz, pisolitic limonite. 

Borsa'ure, boric acid. 

Brauneisenstein, limonite. 

Brechungsverhaltnis, refractive 

Bruch, fracture. 

Bruchig, clastic, fragmental. 

Bruchstucke, fragments. 

Chemise he Verwandtschafts- 
krafte, chemical affinity. 

Daohschiefer, roofing slates. 
Dachziegelartig, imbricated, 

Dampfsporen, gas inclusions. 

Darg, peat formed from marine 

Decke, sheet or cover (e.g., lava- 

Diabasisch-kornige, ophitic. 

Dichte, density. 

DiChtebestimmung, determina- 
tion of density. 

Dick-schieferig, thick-bedded. 

Differenzierung, differentiation. 

D i si ocat i o ns met a mor phi sm us , 
dynamic metamorphism. 

Doppelbrechung, double refrac- 

Doppelgang, composite dyke. 

Dreiwertig, trivalent. 

Druck, pressure, compression. 

Dunn-schlefenig, thin-bedded. 

Dunnschliff, thin section. 

Ourchgreifende, intrusive. 

Durchsichtig, transparent. 

Durchtrankung, saturation. 

Durchwachsung, intergrowth, 
interpenetration, as in graphic 

Ebenschieferig, even-bedded. 
Edelsteinsande, gem sands. 
Eigenschaft, property. 
Einfall, dip. 

Eingesprengt, disseminated. 
EinSChlusse, inclusions, in either 

minerals or rocks. 
Einschmelzung, assimilation. 
Einsprenglinge, phenocrysts. 
Einwertig, univalent. 
Eisener Hut, gossan. 
Eisenoxyd, ferric oxide. 
Eisenoxydul, ferrous oxide. 
Endogene Einschlusse, cognate 

inclusions, autoliths, enclaves 


Entgasung, exudation of gas. 
Entglasung, devitrification. 
Erdharz, Erdpech, bitumen, 





Erguss, effusion. 

Erkennungsmittel, determinative 

ErlanfelS, basic granulite. 

Ersetzung, replacement, metaso- 

Erstarrend, solidifying, crystal- 

Erstarrungsgesteine, igneous 

Eruptivdecke, lava-sheet. 

Erz, ore. 

Erzader, mineral lode or vein. 

Exogene Einschlusse, accidental 
inclusions, xenoliths, enclaves 

Explosionsrbhre, volcanic pipes. 

Fahlbander, banded or foliated 
rocks impregnated with sul- 

Fallen der Schichten, dip of 

Falsche Schieferung, false cleav- 
age or bedding. 

Faltung, folding. 

Feuerfliissig, molten. 

Feuerton, fireclay. 

FHzartig, fllzlg, felted (applied 
to felt-like aggregates of 
minute elongated crystals) . 

Fiaserig, "flaser"; lenticular 
structure of dynamically meta- 
morphosed rocks. 

Fleckschiefer, spotted slate. 

FIBtz, seam, e.g., coal-seam. 

Flugsand, blown sand. 

Fluss Kieselsaure, fluo-silicic 

Fluss-saurc, hydrofluoric acid. 

Forellenstein, 'troctolite. 

Frittung, fritting, partial fusion 
of country rock by volatile 

Fruchtschiefer, knotted slate, in 
which the spots vaguely resem- 
ble ears of corn. 

Gang, dyke, vein, or lode. 

Gangauslaufer, apophyses. 

Ganggefolge, suite of related 

Ganggefolgschaft, differentiated 
series of dykes. 

Ganggesteine, dike rocks. 

Gangulmen, walls enclosing a 
dyke or lode. 

Gangwande, selvage of a dyke 
or lode. 

Garbenschiefer, spotted slate or 
schist, in which spots have a 
sheaf-like form. 

Gebirgsbildende Prozesse, eroge- 
nic processes. 

Gebirgsdruck, orogenic pressure. 

Gediegen, native (as applied to 

Gefaltet, folded. 

Gefrierpunkt, freezing-point. 

Gehangeschutt, talus. 

Gekammerte Spheruliten, hollow 
spherulites, or lithophysas. 

Gelenkquarz, flexible sandstone. 

Gemengteil, constituent. 

Gemischte Gange, composite 

Gepresster Granit, foliated 

Gerblle, pebbles or boulders. 

Gerichteter Druck, directed 

Geschiebe, angular debris, scree 

Gestein, rock. 

Gesteingase, magmatic gases. 

GesteinsbruchstUcke, rock-frag- 

Gesteinslehre, petrology. 

Gesteinsserie, Brogger, 1894. A 
series of related igneous rocks 
possessing certain chemical, 
mineral and textural features 
in common, and exhibiting to- 
gether a continuous variation 
from one extremity of the 
series to the other. 



Gestreckte, linear (applied to the 
texture of foliated rocks) . 

Gestreift, striated. 

Gestrickte Formen, skeleton cry- 

Gestrickte Struktur, netted struc- 
ture (in serpentine formed 
from augite) . 

Gitterstruktur, lattice structure 
(in serpentine, derived from 
hornblende) ; cross hatching (in 
microcline) . 

Glanz, lustre. 

Glasglanzend, of vitreous lustre. 

Gleichgestaltet, isomorphous. 

Gle'-chmassig kornig, even 

Gleichmassige Gesteine, rocks 
of uniform grain. 

Gleitflachen, gliding planes. 

Glimmer, mica. 

Granat, garnet. 

Grand, gravel. 

Granoblastische or Pflaster 
Struktur, mosaic texture. 

Griffelschiefer, pencil slate. 

Grundteig, matrix. 

Griine Schiefer, chlorite schists 
and allied metamorpliic rocks. 

Grus, granitic sub-soil. 

Halleflinta, a banded granulite, 
having the composition of a 

HSrte, hardness. 

Hauptbruch, master joint. 

Hauptgemengteile, essential or 
major constituents. 

Helizitische Struktur, helicitic 

Herausgelost, dissolved or leach- 
ed out. 

Hitzewirkung, action of heat. 

Homooblastische Struktur, equi- 
granular texture. 

Hornstein, chert and allied sili- 
ceous rocks. 


Intrusivlage, intrusive sheet or 

Injizierter Schiefer, injected 

schists or gneisses. 

Kail, potash. 

Kalkabsatze, deposits of CaCO a , 
calcium carbonate. 

Kalkspat, calcite. 

KalktUff, travertine. 

Kalziphyr, calciphyre. 

Karstenite, anhydrite rock. 

Kaolinbildung, or Kaolinisle- 
rung, kaolinisation. 

Keilartig or Keilfbrmig, wedge- 

Kelyphitrinde, kelyphytic border. 

Kies, coarse sand, fine gravel. 

Kelsader, quartz-vein. 

Kieselconglomerate, pudding- 

Kieselerde, siliceous earth. 

Kieselguhr, diatomaceous earth. 

Kieselsauregallerte, gelatinous 

Kieselsaure, silicic acid. 

KieselStein, pebble, stone, flint. 

Kieslagerstatten, pyritic deposits. 

KleinkrystalHn, microcrystalline. 

Klingstein or Klinkstein, phono- 

Klemenfiisser, brachiopod. 

Klttfte, joints. 

Kluftfliichen, fracture-planes. 

Knochenbreccie, bone-breccia. 

Knollen, nodules. 

Knotenschiefer, spotted shale 
or slate (in the outer part of a 
metamorphic aureole). 

Kohlenstoff, carbon. 

Kohlenstoffhaltig, carbonaceous. 

Kohlensaure, carbonic acid. 

Kohlige Substanz, carbonaceous 

Kontraktions-spalte, shrinkage 



Kornig, granular. 

Kreuzschichtung, cross-bedding. 

Krummschieferig, sinuous or 
wave-like lamination. 

Krystallgestalt, crystal form. 

Krystallkern, nucleus of crystal- 

Krystallskelette, skeleton cry- 

KiigelChen, spherulites. 

Kugelgranit, orbicular granite. 

Kugelige Absonderung, spheroi- 
dal partings of igneous rocks. 

Kugelige Verwitterung, spheroi- 
dal weathering. 

Kuppe, puys, domes. 

Lage, bed or sheet. 

Lagenstruktur, lamination. 

Lagenformig, banded. 

Lagergang, sill. 

Langenschnitt, longitudinal sec- 

Lehm, mud. 

Lehmig, argillaceous. 

Lepidoblastische or Schuppige 
Struktur, flaky structure. 

Linsenformig, lens-shaped. 

Lbcherig, pitted, porous, per- 

Lockere Ablagerungen, loose 

Losung, solution. 

Lotrohr, blow-pipe. 


Magmatische Spaltungsprozesse, 

magmatic differentiation. 
Magnet kies, pyrrhotite. 
Mandelformig, amygdaloidal. 
Mandelsteine amygdaloids. 
Marmorisirung, metamorphosis 

of limestone to marble. 
Maschenstruktur, mesh structure 

(in serpentine derived from oli- 


Massenausbriiche, fissure erup- 

Meeresabsatze, marine deposits. 

Mehlsand, silt. 

Merge!, marl. 

Mikroscopieren, to examine 

Mineralbildner, mineralisers. 

Mineraltrennung, separation of 

Mischbarkeit, miscibility. 

Mischgesteine, migmatites, hy- 
brid rocks. 

Mischkristalle, mixed crystals 
(i.e., with isomorphous sub- 
stances in solid solution) . 

Monomineralisch, consisting of 
but one mineral. 

Mdrtelstruktur, mortar texture. 

Mulde, syncline. 

Murbrukstruktur, mortar tex- 

Muschelig, conchoidal. 

Mutterlauge, mother-liquor. 

Nachschube der Spaltungsges- 
teine, subsequent intrusions of 
differentiated rocks (comple- 
mentary dykes). 

Nadelchen, needle (acicular 

Natron, soda. 

Nebengemengteile, accessory or 
minor minerals. 

Nebengestein, country-rock. 

Nematoblastische or faserige 
Struktur, fibrous texture. 

Neugebildet, secondary, authig- 

OberflSchengesteine, volcanic, ex- 
trusive, or effusive rocks. 

Objekttrager, microscope-slide. 

Oelschiefer, oilshale. 

Orientterter Druck, directed 
pressure, stress. 




Pechstein, pitchstone. 

Pflasterstruktur, mosaic tex- 

Pietrokristallisation, crystallisa- 
tion during powerful lateral 
pressure (applied to the forma- 
tion of the central granite of 
the Alps). 

Plattchen, lamina. 

Plattige Verwitterung, platy 
weathering seen on the exposed 
surface of certain igneous 

Plattig-schieferig, laminated. 

Pleochroitische Hdfe, pleochroic 

Poikiloblastische or helizitische 
Struktur, helicitic texture. 

Porphyroblastische Struktur 
pseudo-porphyritic texture (in 
metamprphic rocks, due to the 
presence of relatively large 
crystals which have developed 
in the rock by recrystallisa- 

Putzen, xenoliths or cognate in- 

Quadern, flags; term applied to 
flaggy rocks and to those 
which can be quarried in 
blocks of cubic or rectangular 
prismatic form ; freestone. 

Quaderstein freestone. 

QuartZ-Keil, quartz wedge. 

Quellkuppe, lava dome. 

Querbruch, transverse fracture. 

Querschlagig, transverse. 

Quetschflache, crush plane. 

Rand, edge, periphery. 

Randfaoies, marginal facies (e.g., 
of an intrusion). 

Rauchkalk, magnesian lime- 

Reibungsbreccie, friction-brec- 

Reibungsflachen, slickensides. 

Reihenfolge, sequence. 

Reihenfolge der Kristallisation, 
order of crystallisation. 

Reihenfolge der Schmelzbarkeit, 
order of fusibility. 

Reisenkbrnig. very coarse 

Richtung, direction. 

Roggenstein, oolite, roestone. 

Riickstand, residue. 

Rutschflachen, slickensides; 
gliding planes in minerals. 

Sahlband, selvage of a vein or 

Salzsaure, hydrochloric acid. 

Sanduhrstruktur, hour - glass 

Sattel, anticlines. 

Sattigungspunkt, saturation 


Sauerstoff, oxygen. 

Saulige Absonderung, columnar 

SaurstOff, oxygen. 

Schalige Abblatterung, spheroi- 
dal exfoliation. 

SchaHge Verwitterung, spheroi- 
dal weathering. 

SchalStein, sheared tuff, gener- 
ally basic or calcareous. 

Schicht, bed or layer. 

Schichtflache, bedding or schis- 
tosity planes. 

Schichtgestein, stratified rock. 

Schichtung. bedding or strati- 

Schieferung, cleavage (of rocks). 

Schieferig, slaty, foliated, 
lamellar, schistose. 

Schieferton, shale. 

Schiefwinklig, oblique. 

Schiller, the shining lustre of 
minerals such as hypersthene. 



SchiiDerfels, serpentine contain- 
ing bastite. 

Schillerspath. bastite. 

Schizolithe, diaschistic or dif- 
ferentiated dyke rocks. 

Schlackenlava, scoriaceous lava. 

Schlamm, mud, silt, ooze. 

Schlammen, to elutriate. 

Schliege, concentrate. 

Schlieren, streaks in igneous 
rocks differing in texture and 
composition from the normal 
mass of the rock, but without 
sharply marked boundaries. 

SchmeizflUssig, molten. 

Schmelzfluss, melt, or fused 

Schmelzwarme, latent heat of 

Schmelzpunkt, melting point. 

Schmelzlosung, molten solution. 

Schmelzung, melting. 

Schollenlava, block lava. 

Schotter, shingle. 

Schiippchen, scale of film. 

Schwefelkies, pyrite. 

Schwefelsaure, sulphuric acid. 

Schwefelwasserstoff, sulphur- 
etted hydrogen. 

Schwerkraft, gravitation. 

Selfen, gem sands; placers. 

Seigerung, liquation. 

SeitencJruck, lateral pressure. 

Schotter, shingle. 

Siebstruktur, sieve texture. 

Siedequelle, geyser. 

Sippe, tribe, series, e.g. " Atlan- 
tic " and " Pacific " series. 

Smirgel, or Schmergel, emery. 

Sonderung, sorting out. 

Spaltbarkeit, cleavage (of 
minerals) . 

Spaltungsgesteine, differentia- 
tion rocks. 

Spaltungsvorgange, differentia- 
tion processes. 

Spezifisches Gewicht, specific 

Spratzige Lava, Aa-lava. 

Spreustein, zeolite. 

Sprodigkeit, brittleness. 

Sprung, fissure. 

Stachelhauter, echinoderms. 

Steinkohle, coal. 

Steinkohlenflotz, coal-seam. 

SteinwulSt, nodule. 

Stellvertretendo Gementeile, 
" substitute " constituents 
(e.g., sodalite in place of 

StickStOff, nitrogen. 

Strahlstein, actinolite. 

Streckung, parallel or fluxion 
structure (extension of 

minerals along roughly paral- 
lel lines due to flow or 
recrystallisation) . 

Streichen der Schichten, stri! e 
of strata. 

Strengflussig, refractory. 

Strom, lava stream or flow. 

Tafelig, tabular. 
Tegel, brick-earth. 
Teig, paste, magma. 
Teilmagma, partial or fractiona 1 



Ton, clay (often used in com- 
bination \vith another noun, 
or preceded by a specific adjec- 
tive which gives the composi- 
tion, e.g., Tonsckiefer = c\ay- 
slate ; Kaolinisher Ton = 

Tonerde, alumina. 

Tonig, argillaceous. 

Transversals Schieferung, trans- 
verse cleavage. 

Tropfstein, stalactite. 

Trtimer, vein or dyke. 

Trummer, debris. 

Trummergesteine, clastic rocks. 

Tutenmergel, cone-in-cone struc- 


Ubergangsglieder, transition- 
types or members. 

Ubergemengteile, secondary * 

Ubersattigt, oversaturated. 

Uberschiebung, overfold. 

Umbildung, alteration, recon- 

U mlagerung, rearrangement ; 
paramorphism ; migration. 

Umkristallisation, recrystallisa- 

Umwandlung, alteration. 

Ungeschlehtet, unstratified, mas- 
sive., insoluble. 

Unmischbar, immiscible. 

Urgebirge, fundamental crystal- 
line formations. 

Urschiefer, primeval schist. 

Urspriinglich, original, primary. 

Verbandsfestigkelt, cohesion. 
Verbindung, combination. 
Verdrangung, replacement. 
Verfestigung, consolidation. 
Vergrosserung, magnification. 
Verhartung, induration. 
Verkieselter Hornfels, silicified 


Verkieselung, silicification. 
Verkittung, cementation. 
Verruschelungszone, crushed 


Verschlebung, displacement. 
Verschweiste Gange, welded 


Versuch, experiment. 
Vertikale Belastung, vertical 


Verwachsung, intergrowth. 
Verwerfung, fault. 
Verwitterung, weathering. 
Verwitterungslbsung, solutions 

produced during action of 


Verwitterungsprodukte, pro- 
ducts of weathering. 
Verzahnte Struktur, sutured 


VerzwilUngt, twinned. 
Vollkrystallinisch, holocrystal- 


Vorgange, processes. 
Vorherrschend, predominant. 


Wacke, weathering residue of 

subsilicic igneous rocks. 
Wanderblock, erratic. 
Warmbrunnen, thermal springs. 



Wasserstoff, hydrogen. 

Wechsellagern, interbedded. 

Weichtiere, mollusca. 

Wellenfurchen, ripple-marks. 

Wesentliche Gemengteile, essen- 
tial constituents. 

Wirkung (z.b. der Mineralbild- 
ner), action (e.g. of minerali- 
sers) . 

WUstensand, desert sand. 

Zeichenschiefer, pencil-slate. 

Zerfressen, corroded. 

Zerkliiftung, fissure, joint. 

Zersetzung, replacement of a 
mineral by decomposition pro- 
ducts other than those due to 

Zertrummerung, disintegration. 

Zonarer Aufbau, zonal structure 
(in crystals). 

Zuckerkornig, saccharoidal. 

Zufuhrkanale, feeding channels. 

Zugefuhrte Gemengtelle, sec- 
ondary minerals (whose for- 
mation involves the addition 
of material from external 
sources, e.g., tourmaline). 

Zusammensetzung, composition 
(mineral or chemical). 

Zweiwertig, bivalent. 

Zwischenformen, passage-types. 

mesostasis (interstitial mat- 

Zwischenmasse, cement. 

Zwischenraume, interstices. 




(an anderen Orten), 

elsewhere, or 

(am angefiihrten Orte), 

loc. cit. 



atomic weight. 






in reference to, etc. 

bezw., bzw., 

(beziehungsweise) , 







such like. 


(das heisst), 

that is to say. 


(das ist), 

that is, i.e. 


(Handschrift) , 

manuscript, MS. 


(siehe oben), 

see above. 


(sogenannt) , 



(siehe unten\ 

see below. 


(unter anderen), 

among others. 


(und ahnliches mehr), 

and the like. 


(und andere mehr) , 

and others, and so on 


(und ofter), 



(und so fort) , 

and so forth. 


(und so weiter). 

and so on, etc 





(/urn Beispiel) . 

for example, e.g 




not, without 


a river in Sicily 

close, dense 

God of the winds 


a point 

a ray, spoke 

elsewhere, otherwise 

alien, foreign 

about, around 
| doubtful 
I an almond 

towards, up to 


near at hand 
to deceive 

(derived) from 
an offshoot 
first cause, origin 

a wedge 
an axle 


a test, means of 

trial (touchstone) 

an arrowhead 
a bud, sprout 

amorphous, a$hamtic, 

anhedral, asphalt, 
abyssal, hy-pabyssal. 

actinolite f stalactite, 
allotro-py, allogenic, 

allothi genous . 
anamesite, anamorphism, 

anthracite, anthraxolite. 

apo-rhyolite, a-po-phyllite. 
autoclastic, autoHth, auto- 

mor-phic, authigenous. 








a bunch of grapes 






to hold 


Chi, x 

a Greek letter (ch) 









Cry os 





chrysotile, chrysolite. 


a finger 

dactylitic, dactyloty-pe. 


a tree 










diablastic, diagenesi* 

diaschistic, diatrenn 




a crossing over 



an interchange 



to delimit 


Dis, di 

twice, double 

disthene, dimorphism. 





an old tree (e-g-, 


with fungus-lined 


EC, ex, exo 

out from 

exogenetic, exomor-phisn 



amygdaloidal, granitoid 


a choice selection (of 


colours or min- 

erals ?) 









endogenetic, endometa- 



an adversary (to 





e-piclastic, e-pidiorite, 




euhedral, eu-photide, 

eutaxitic, eutectic. 


easily discerned 



to flow well 



hospitable (rich in 




the earth 



a race, a kind 

homogeneous . 




G rap no 









Hyp, hypo 


I sos 


















to beget 



glauconite, glauco-phane. 

I write 

gra-phite, gra-pho-phyre. 




halite, halogen. 


ha-plite, a-plite. 




heterogeneous, hetero- 



holo crystalline. 

the same 



hydr other mal, hydato- 


under, nearly, less 

hypabyssal, hypidio- 


mor'pJiic, hypogene. 
hy-perite, hy-persthene. 


hystero crystallisation. 

one's own 


the same 

isomor-phous, iso-pachyte, 


down from, down 

cataclastic, katagneiss, 

a rind, shell 


a horn 



clastic, diaclase. 

I incline 

microcline, syncline. 

a berry 






a mixture 
I dominate 

melanocratic, leucocratic. 

a thread 



crypto crystalline, crypto- 






a cistern 


a scale, flake 



leucocratic, leuco-phyre, 

leucoxene, leucite. 




a rock 

lithology; -tie (suffix in 

rock and mineral 

names) ; -ith (suffix in 

terms such as batho- 

lith, laccolith, denoting 

mode of occurrence). 


a discourse 



a basin 



a loosening 






large, long 



a pearl 




me gas co-pic. 



meionite, miocene. 



melanite, melanocratic, 



a part 




anamesite, me socratic, 

mesolite, mesostasis. 


after (signifying a 





microcrystalline, micro- 



a mixture 







amorphous, allotriomorphic. 

met amor phi c, idiomcrphic. 

My Ion 

a mill 

my I o nit e. 


an ant 



a fibre 



a cloud 



a house 



small, few 

oligoclase, oligocene. 


an egg 



a serpent 

ophicalcite, ophite. 


to see 



straight, rectangu- 

orthoclase, orthogneiss. 

lar, regular 


a scar 



sour, acid 



to smell 




old : palao-picrite. 


-palingenesis, -palimpsest. 




-par agenesis, -paragneiss, 

-p ar amor -phi c. 

a framework 








a rock 


a lentil 


I show aphanitic, phenocryst, 



phanero crystalline. 







a leaf 

-pJiyllite, apophyllite. 

of a reservoir 


to produce 
a stream, jet 




to press together 

-pi ezo crystallisation. 

a felt -pilotaxitic, hyalopilitic. 

a pea ! -pisolite. 

slanting, oblique 


a moulded image 






full, many 


the God of the I plutonic. 


vapour ; pneumatolytic. 

spotted poikilitic. 

many -poly genetic, polymor- 


purple, reddish \ -porphyry. 


proto clastic, i>rotogir:e 





a pebble 





-pyro clastic, -pyromeride, 

pyroxene, pyrolnsite. 

a blanket 


to stream 





a plank, table 




schist, aschistic, dia- 









a shadow 



to look at 

megascopic, microscopic. 


a body 



to slip 



a wedge 






that which drops 



to fall in drops 



a cross 







asthenosphere, disthene, 


to glisten 



a colonnade 



a layer 



a pillar 









a meeting together 







ataxite, eutaxite. 


a builder 

eutectic, tectonic. 








eagerly sought 




thermal, tlier mo dynamic. 





a hole 

diatreme, trematoblastic. 





a nibbler (e.g. trout) 



a turn 

allotropy, isotro-pic. 


smoke, a cloud 



a stranger 

leucoxene, Pyroxene, 



I boil 


26 3 



from, away 

ablation, abrasion, agglo- 


a needle 




to wash upon 






together, with 

concretion, comagmatic, 



a crown 



calcrete, concrete, concre- 


away from 

dedolomitisation , detritus. 

to lay bare 
to harden 



effusive, ejectamenta. 

a thread 
to become 
a flux 

silicified, vitrify, 

a river 

1 ~ 


a leat 


to gather in a heap 

agglomerate, conglomer- 


a grain 

granite, granular. 



to throw in 

intercalate, intersertal. 





a lake 
a little stone 
a brick 
to wash 



to shine 



a razor 



an olive 
a small orb 

o If vine. 



a little time 

penecontem-poraneous . 


to break back 
to gnaw 



apart from 
a partition 
a serpent 
I insert 

silica, -petrosiler 


to rub 
to thrust 

detritus . 



ultrabasic, ultramela- 


smallpox, pitted 
a worm 
bird lime 





Rocks and Ore-deposits 266 

Igneous Rocks : * 

1. Oversaturated : characterised by quartz 268 

II. Saturated - 270 

III. Undersaturated : characterised by olivine ... 272 

IV. Undersaturated : characterised by felspathoids 274 
V. Undersaturated : characterised by felspathoids 

and olivine 276 

Products due to Igneous Exudations ,. 278 

Metamorphic Rocks . . 280 

Exogenetic Rocks ... 282 

Meteorites (Dr. G. T. Prior, F.R.S.) 284 

* In these Tables the names of leucocratic rocks are printed in 
italic, and those of melanocratic rocks in heavy type. See also 
A. Johannsen : Journ. Geol., xxviii, 1920, p. 38, for a discussion 
of classification and nomenclature that has appeared since the 
pagination of this book. 




Formed by processes of internal origin, which 
processes operate deep-seatedly or from within out- 
wards. High temperature effects constitute the 
prevailing characteristic, and the water taking part 
as an agent is partly of magmatic origin. 

1. Igneous Rocks and Segregations. 

2. Igneous Exudation Products. 

(a) Contact impregnations and metasomatised 
rocks, including pneumatolytic rocks and 

(b) Hydrothermal vein rocks and deposits. 

(c) Solfataric deposits. 

3. Thermo -dynamically Altered Rocks and 

* See T. Crook : Min. Mag., xvii, 1914, pp. 73-4 and 84. 



Formed by processes of external origin, which 
processes operate superficially or from without in- 
wards. These rocks are formed at ordinary or com- 
paratively low temperatures, and the water taking 
part in their formation is of atmospheric origin. 

1. Weathering Residues. 

2. Detrital Rocks (including Placer Deposits), 
comprising- aeolian, alluvial, and marine sedi- 
ments, loose or cemented. 

3. Solution Deposits, loose or cemented. 

(a) Surface Solution Deposits. 

(i) Inorganic deposits, 
(ii) Organic deposits. 

(b) Percolating Solution Deposits. 

(i) Certain vein deposits and cavity infill- 

(ii) Metasomatic rocks and deposits, and 
secondary enrichments. 

4. Accumulations of Organic Matter and their 

(a) Carbonaceous. 

(b) Bituminous. 







| |s 

2 & 


-J ' 




's E 


^"v S 

3 Orthoclase 
3 < Albite 

'rcenite. Arizonite. 
natite. Graphic Gran 
I Tsingtauite. Muscov 


Kfe. Alsbachite. Bei 
phyre. Quartz-porph 



Pegmatite. Graphic 
Granite. Granitite. < 

Granite-porphyry. Qua 
Granophyre. Microgra 

Rhyolite. Liparite. 
Nevadite. Quartz 
Pyromeride. Masa 



<x, o 

^ -elf 

s * 


'it ^? 

oi <U "^ 

S oj ^ 

' 5 'C fl> 


S Jr*\ 

o -i CX 

o .ti r, ii > 



thfieldite. Alaskitt 

:ali-granite. Ekerite, 
rordmarkite.) (Ever^ 

uartz-lindoite. Quartz-b 
e. Grorudite. Paisan 
Ailsyte. Ekerite-por 

ite. (Taimyrite.) 

Masanite. Winds 
e. Quartz-monzon 
Adamellite. Vaugm 
Rapakivi. Unaki 

Markfieldite. Routi 

Dellenite. Toscar 

E -S ^^ 

O^ ^* 


<> .-H 


i ~ 

a & 



CO t"^ 


r^^ O 

<D CH 

"o >, 







"^r 1 ? ** 

s -^ 





o J 



.5 ? 

-M tn 

5 <| 



*O flJ 


rt .- 
tJ C .0 a 

- rf <a c3 -5 

. --gQ e 




Q 4 

^3 * 

3 . 

rt oJ 

2 5 


J s 


3 "c3 X! 


C/3 13 



c | 




H , 



1 1 





asuiooSno eujsepuv 





. '3 


"S ~ tn 

iS 3 H 

' G >> 

? XI OJ 

|J || 

a l.g 



I'S 'Ss ^ 

1|fl o| S 


a? * 

^i I'l "1, 
2 1> ^ # 

o c* o K -^ 

?> rt 

rf "^ 

: ,0 D 4> T3 rt 


II 1 

' ? >! 'o N *V 

3 *J 

si Is 1 


rt ^ b O2 3 

art ^ ^*o 

r-* N*^ 

^a a 

9){40pBJqBl 8)!UMO)A8 


}U9sqe sjedsidd 















^Q "tl 



. 3 w .r" 

S -G 

o 5 



"i ^"^ * 




II > 

"S 43 



u> E ^ 


rt .0 =j 




-i H 

JS .22 

N "-' "o 

K*^t *" 


* f^ 

43 C 





& C^ 



+J *^ 









| . 



r3 ** 











s.s | 


S * <u 

1 . 

i & 

^ CD 

.^ _n 



1 1 


. Pulaskite. Ump 
tanite. Hatherlite 

Lindoite. Lestiu 
te. Rhomb-porpl: 

>ellite. Kenyte. 

nzonite(inpart). > 
Mangerite. Tonsl 


:e-porphyry. Mae: 

> Q 




-55 M 

<^:S -^ 






?" ~ ^ 


. 'cl 






( ^ rf 

"C -^ 2 


*' *H d 


O ( O 


o ^ * 

6 -g 


-2 -2 

fi <u 

'5b ^ 

^'So'S ^ 

^ .ti 




.S S 

J2 c B 

1 :i 

^ h-rv 

^JC^)^ c 

! ^ 

^ ^J . 

*^ 3 J2 ' 
^ . *CU 



I 5 


O/S <u 



Sit: 3 
^H M 


cu l_ -2 0) 
5'"^ to 





.1* 3 J 

'* & S 


f2 JM 

^cj :*-! 
^ W 

1 1 

43 *" 

W S 

S5 342 


sf^ 5 | 

| < 




s* c 

o o'SH 




rvE fl 


^'l ; l 







asB|oo8[io aujsapuv 















J | 


O l-i 


o ^ 


N O 

TD re 


c u 

OH ^ OJ 

^> C3 


^ re +* 

r^H Ct 


^ 2 





-2 o 



5 2 









S I 

'<, *;?. i^aoraaonte Rock. 
ro. Hyperite. Norite. 
dite. Issite. Bojite. Corsite. 

ite. Diabase. Ophite. 
:e. Algovite. Vintlite. 
latinite. Anamesite. 
Camptonite. Tops 

itorinite. Labradorite. 
Tholeiite. Miharaite. 
rite. Alboranite. Nonesite 
rgite. Variolite. Sudburite 
3. Soggendalite. Arapahite. 

//uft'/tf. Anorthite Rock. 
Kedabekite. Kyschtymite. 

Dranite. Cumbraite. 

e. Pyroxenolite. Diallagite. 
. Hypersthenite. Websterite. 
Oavainite. tAvezacite. 
lendite. Amphibolonte. 
Griquaite. Newlandite. 
e. Ostraite. Rodingite. 



5 ^Q re 

!H .-. 03 

^ -t-> Q ^ ** 

S - & 

2 * "^ " 


-J re Q 


'5 'S -i 

M ; 






juasqe sjBds 




o i o 



-g 8 

13 'S 

> S 







BSB|008l.lO 9UIS9PUV 



2 -cS 

.-, 0) O jj 

| Id 

G >v" G S 

cfl "^ 

c -V oj J o 

.1 .' ^ 

o 5.g 


s 1 

0, o 

. 5J . & 

IP i. i 

.5 ^2 
iS^ 11 ^ 5 

>'g^ 13 c 

i*K s i i : 

te. Rougemontite. 
laite. Olivine- 


2 2* " ~ " 

u | 

<= .22 -gflj 2 

\&l !i 1 I 

5^1 II 1 

1 s I I 

.>> .> 

o 5 

Allivalite. Oueni 
Harrisite. Ti 


I'lSS .'=! >1 "E : 

?.il\it li i 

H i 


< (XaOSS3OO'B JO) 

juasqB sJBdsiaj 








I 5 



-^ ."S 



CX 1 -22 a) ' -* rti 




1 1 1 ll 





i ' 1 ? ^ 2 



c/) j - (3 jy s . y 



+ : p O O '3 
o 0) T3 



J 3 <M 


1 "| J M 







^|j ^J ^ . QJ ^j 

g a> . 'C 15 ^ -^ "5 'So -^ 





<u">, rt'"' : ''5 o 




thoclase + Leucil 

+ Soda-felspath 

iwl^5 u 1.5 

*t3 j <n^ Q? . '5. 

co aj a> .ti '2 aj -^ 'E * - c5 '-2 


te. Nosean-phi 

rdalite. Canad 








o| .slJ si 

ll 1 IflUlI 11 









g, * <J C >. be 1 = tuo^ 

a> vJ - ^ < ^ 2 S c^ 
2 Q<< * H 






-H | 

S o 


-2 G 


1 a - 


a 2 ^ 

tt; S) 


-S . 8,S 





<*-! S 3 




rt 'C.rt 












+ j 




^ ^/5 




,, WI V 

9se|9o9i|o auisapi 





<u" '^3 

.-S 3 






U . 



. ^j 





.'tn Q3 

1 H O 





w 1 


<u 'C 

ite. Ordanchite. 


jopejqei aifUMOiAg 

'5 2 

1 1 

? I 



$ .i 

o r5 

0) <U 

J l u 

QJ - 3 
*t5 *^n *^ ""^ 


<J ^s a 3 

3 S -v 

1 | 

_N ^H 

Hi ,i i 1 1 
'i !. :ii i* I 

.-Sl .SS -S"- ! 3.5,jS 
| s -5 ffi-S^-n 

1/5. 1 Srf , If, 

% S H .Ss ^ ^ S a 

^'H I 2|" a 1 

I . s &c ^ I | 
fc.3- 1 ^1 ^ S m 

s ~ m Z c3 

O _O Q 


, ' (AJOSS90DB JO) 

iuasqe SJedsiaj 

2 7 6 

























: + Leuc 

Is 5 


3 -Ms I 




rt ; a 




tw i 

'3 c 

1 I 


1 < 















1 : 








asBiooSno auisapuv 























o ^ 



c rs 


.^ fi 












i J 



< 03 

5 oJ Jj 






l r^ 


C T3 


CB */n 


" rt'C 

a I 

.tr E g o5 


jfl u | 


1 1 5 | 

o Q3 


OJ W (^ 

il 1 

.5 c 

5 ^ *^ 




o 11 " | 









juasqe sjBdsiad 




Materials^ Introduced. 


Alteration Types. 


Volatile compounds 


Schorl Rock. 

of boron with a cer- 


tain proportion of 

Tro wleswor thite . 

fluorine compounds. 


Do, with iron com- 


pounds when associ- 


ated with garnetisa- 




Greisenisation or 

Fluorine compounds. 

intrusions. < 



Water and carbon 

Kaolin. China-cla; 




Silica, water, sul- 


phides, and fluorine 



Iron compounds, and 




Garnetised igneous 



Scapolitisation or 

Volatile compounds 
of chlorine, titanium 


norite, and 

Scapolitised rocks. 
Kuskite, Yentnite. 

and phosphorus. 


Hornblende - scapoli 


Water, carbon-diox- 




ide, and sulphides. 
Water, carbon-diox- 


Quartz-sericite rod 

ide, and potash- 


. compounds. 

and related 


Water, sulphides, and 



iron compounds. 
Water, sulphates, and 


Quartz-alunite rocl 




Silica, water, sul- 

dolerite) . 

phides, sulphates. 


Silicified rocks. 



1 1 


Epidotisation or 

| Water, carbon-diox- 
i ide, sulphides. 

1 Gabbro. 
r Dolerite. 





Do, in solutions rich 



in sodium and iron. 




Zeolites, silica anc 


basalts. Melaphyre 

Serpentinisation Water, sometimes 


Serpentine Bowenit 
Chrysotile -asbestos 





Alteration Types. 

Associated Ore- 



Tourmaline - hornfels 

1 Cassiterite- 




and schist. Quartz- 

wolfram lodes. 

arenaceous -\ 

tourmaline rock. 


Tourmaline - corun- 


dum rock. 







copper lodes. 




Greiseeiisation or 



Sulphides gener- 


ally, especially 

copper sulphides, 


Garnetiferous green- 

and magnetite 





Various types of Gar- 


netiferous skarn. 



Scapolite-marble and 
lime-silicate rocks. 

Titaniferous mag- 
netite, ilmenite, 

Scapolitisation or 

and apatite. 

-i Tertiary gold and f 


silver lodes. 




gold deposits. 



(PRand gold < 



(? Banket, in part). 


Quartz-alunite rock. 

Copper- gold 




Chert, phtanite. 




Quartz-bary tes-rock . 





> Chlorite-schist. 

\ ( 


Vrg llaceousJ 

j Chlorite-epidote 

V deposits. j 


Epidotisation or 






/ x 

Native copper 





i" nisi 

by Igneous 

2 2 .5*3 

3? 8 S 

5 rt i^J 

s s B81 

j ,-s *3 ^ 

3 S C -M 

il 61- & 

o j, . i g 

QJ rt E & 




'g 1 1* I II .1 1 I 

iS 9 "S &P.^. 'I 2 I 


Banded o 



*-" !3 


I s 

a&^a-^ ' 



en ,J i 


2 'i ^ '2 

W I^H M (LI ^ 

-2 .2 -Q - 5 g 

i^J |||| 

III loo- 2 



6 . 








I.I |s loi.S'1 






^3 w>'5b 2-2 gg 

S S-0 3&g;5 
05 gw ^Jg 

S_, ^4 

<u ex 


ft ^ 


cn 8 

M . C/5 

1 21 S i i S ; 

C/3 C . "^ 

c tuo-2 cx '-5 'S - '53 .23 .2 
O o -5 S ai -2 oj 2 rf cGSJS 
||?|^|^.g S^^gjS) 

I Ifi^sH 8 till 

'S.a . " o> 

C D D .2 hVi ** 
O' d ,tJ <0 i ^3 
tafi-t; c <u o 
fl) i ro bo*a X) 


05 tl JlJ ^ QJ "^^ ^ ,^"\ JlJ 

_^ ^<U ^ 3 CH j 


u 1 " 1 K 



g ^^-^o^.ti c-^<u 

1 illlllilll 




i giilii'JiJ 


^~* ^ 4n !-i -*^ 5 7*^ CX^ 


u a^ 



. d 


' ' 

^ ^ 

TS \ 

o o ^-*. 




&*'' ft* 

1 iS^ 12 




o ^f ^ 








A rgillaceous. 



Scree ) 
S' Talus 1 
25 Boulders \ 
$ Shingle 
Pebbles f 



C. Breccia. 
Limestone Brecci 
C. Conglomerate 


a; v. Gravel ) 



Coarse Sand 


Residual Sands. 


C. Grit. 

Later! tic Sand. 

CO .^ 

2 ** 

. Felspathic, 


C. Sandstone. 

Quartzose Lat- 

2 a Sand. 
3 5 (Coral Sand.) 
(Volcanic Sand.) 

! Micaceous, 
Glauconiti and 
other Sandstones. 


Gypseous and 
Barytic Sandstone 

^ Silt. 


Adobe. Loess. | Loess. 

Residual Clay. 

Terra Rossa. 


Shale. 1 C. Shale. 

Lateritic Clay 

s . Rock-flour. 




S-S Mud. 
S2 Dust. 

Clay Rock. Argillite. 
^ Pelite. 

(Red Mud.) 
(Green Mud.) 

: (Coral Mud.) 

Fireclay. Fuller's Earth. 

(Blue Mud.) 

5? ^ (Volcanic Mud ) 


^ (Red Clay.) 



Salitie, etc. 

Calcareous, Dolomitic, etc. 

Rock Salt 

Calcareous Tufa. 

Potash and 

Travertine. Onyx-marble. 


other Saline 

Stalactite. Stalagmite. 




Oolite. Pisolite. Pea Grit. 
Magnesian Limestone. 



Dolomitic Limestone. 





Gypsum. Anhydrite. 

Globigerina Ooze. 

Pteropod Ooze. 

Foraminiferal Limestone. 

Nummulitic Limestone. 

(Potash and 

Chalk. Miliolite. 


Iodine Salts 
from Kelp.) 

Coral ' Sands.' Coral Limestone. 
Shell ' Sands.' Shelly Limestone 

Crinoidal Limestone. 

Bryozoal Limestone. 

Algal Limestone. 

etc., etc., etc. 













S. Breccia. 

S. Conglomerate. 
Silcrete. Banket. 

P. Conglomerate. 

F. Conglomerate. 


S. Grit. 

F. Grit. 

B. Grit. 

S. Sandstone. 

F. Sandstone. 

C. Sandstone, 

B. Sandstone 


S. Shale. 

P, Shale. 

F. Shale. 
Pyritic Shale 

C. Shale. 

B. Shale. 





of Organic 






Siliceous Sinter. 

Lake and Be 

>g Iron Ores, 



Brown Coal. 
Bituminous Coal. 
Cannel Coal. 


Diatom Ooze. 
Radiolarian Ooze. 
'Radiolarian Chert. 

Bone Beds. 

Chert. Flint. 

Phosphate Rock. 
Phosphatic nodules. 




. o 5 

<O & 13 

ti po-3 

< i 


(N S 


! o 

3 ri 



. 6 6 ^ 
.s o o <u 

- 1 ^r 
* fiJil 











Thomas Murby & Co., 1, Fleet Lane, Ludgate Circus. London, E.G.4 

Grains from Asphaltic Sandstone, Angola. 
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By S. J. SHAND, D.Sc., Ph.D., F.G.S , Professor 
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A book for those who have never picked up 
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